docs: Add upgrade instructions

Author: Techassi

modules/ROOT/partials/release-notes/release-25.11.adoc

@@ -467,3 +467,144 @@ These OpenShift versions are no longer supported:
 
 * `4.17`
 * `4.16`
+
+==== Upgrade from 25.7
+
+===== Using stackablectl
+
+====== Upgrade with a single command
+
+Starting with stackablectl Release 1.0.0 the multiple consecutive commands described below can be shortened to just one command, which executes exactly those steps on its own.
+
+[source,console]
+----
+$ stackablectl release upgrade 25.11
+----
+
+====== Upgrade with multiple consecutive commands
+
+Uninstall the `25.7` release
+
+[source,console]
+----
+$ stackablectl release uninstall 25.7
+
+Uninstalled release '25.7'
+
+Use "stackablectl release list" to list available releases.
+# ...
+----
+
+Afterwards you will need to upgrade the CustomResourceDefinitions (CRDs) installed by the Stackable Platform.
+The reason for this is that helm will uninstall the operators but not the CRDs.
+This can be done using `kubectl replace`.
+
+// TODO: Mention that the CRDs of the secret-operator don't need to be replaced manually.
+
+[source,shell]
+----
+kubectl replace -f https://raw.githubusercontent.com/stackabletech/airflow-operator/25.11.0/deploy/helm/airflow-operator/crds/crds.yaml
+kubectl replace -f https://raw.githubusercontent.com/stackabletech/commons-operator/25.11.0/deploy/helm/commons-operator/crds/crds.yaml
+kubectl replace -f https://raw.githubusercontent.com/stackabletech/druid-operator/25.11.0/deploy/helm/druid-operator/crds/crds.yaml
+kubectl replace -f https://raw.githubusercontent.com/stackabletech/hbase-operator/25.11.0/deploy/helm/hbase-operator/crds/crds.yaml
+kubectl replace -f https://raw.githubusercontent.com/stackabletech/hdfs-operator/25.11.0/deploy/helm/hdfs-operator/crds/crds.yaml
+kubectl replace -f https://raw.githubusercontent.com/stackabletech/hive-operator/25.11.0/deploy/helm/hive-operator/crds/crds.yaml
+kubectl replace -f https://raw.githubusercontent.com/stackabletech/kafka-operator/25.11.0/deploy/helm/kafka-operator/crds/crds.yaml
+kubectl replace -f https://raw.githubusercontent.com/stackabletech/listener-operator/25.11.0/deploy/helm/listener-operator/crds/crds.yaml
+kubectl replace -f https://raw.githubusercontent.com/stackabletech/nifi-operator/25.11.0/deploy/helm/nifi-operator/crds/crds.yaml
+kubectl replace -f https://raw.githubusercontent.com/stackabletech/opa-operator/25.11.0/deploy/helm/opa-operator/crds/crds.yaml
+kubectl replace -f https://raw.githubusercontent.com/stackabletech/spark-k8s-operator/25.11.0/deploy/helm/spark-k8s-operator/crds/crds.yaml
+kubectl replace -f https://raw.githubusercontent.com/stackabletech/superset-operator/25.11.0/deploy/helm/superset-operator/crds/crds.yaml
+kubectl replace -f https://raw.githubusercontent.com/stackabletech/trino-operator/25.11.0/deploy/helm/trino-operator/crds/crds.yaml
+kubectl replace -f https://raw.githubusercontent.com/stackabletech/zookeeper-operator/25.11.0/deploy/helm/zookeeper-operator/crds/crds.yaml
+----
+
+[source]
+----
+customresourcedefinition.apiextensions.k8s.io "airflowclusters.airflow.stackable.tech" replaced
+customresourcedefinition.apiextensions.k8s.io "authenticationclasses.authentication.stackable.tech" replaced
+customresourcedefinition.apiextensions.k8s.io "s3connections.s3.stackable.tech" replaced
+...
+----
+
+Install the `25.11` release
+
+[source,console]
+----
+$ stackablectl release install 25.11
+
+Installed release '25.11'
+
+Use "stackablectl operator installed" to list installed operators.
+----
+
+===== Using Helm
+
+Use `helm list` to list the currently installed operators.
+
+You can use the following command to uninstall all operators that are part of the `25.7` release:
+
+[source,console]
+----
+$ helm uninstall airflow-operator commons-operator druid-operator hbase-operator hdfs-operator hive-operator kafka-operator listener-operator nifi-operator opa-operator secret-operator spark-k8s-operator superset-operator trino-operator zookeeper-operator
+release "airflow-operator" uninstalled
+release "commons-operator" uninstalled
+...
+----
+
+Afterward you will need to upgrade the CustomResourceDefinitions (CRDs) installed by the Stackable Platform.
+The reason for this is that helm will uninstall the operators but not the CRDs.
+This can be done using `kubectl replace`.
+
+// TODO: Mention that the CRDs of the secret-operator don't need to be replaced manually.
+
+[source,shell]
+----
+kubectl replace -f https://raw.githubusercontent.com/stackabletech/airflow-operator/25.11.0/deploy/helm/airflow-operator/crds/crds.yaml
+kubectl replace -f https://raw.githubusercontent.com/stackabletech/commons-operator/25.11.0/deploy/helm/commons-operator/crds/crds.yaml
+kubectl replace -f https://raw.githubusercontent.com/stackabletech/druid-operator/25.11.0/deploy/helm/druid-operator/crds/crds.yaml
+kubectl replace -f https://raw.githubusercontent.com/stackabletech/hbase-operator/25.11.0/deploy/helm/hbase-operator/crds/crds.yaml
+kubectl replace -f https://raw.githubusercontent.com/stackabletech/hdfs-operator/25.11.0/deploy/helm/hdfs-operator/crds/crds.yaml
+kubectl replace -f https://raw.githubusercontent.com/stackabletech/hive-operator/25.11.0/deploy/helm/hive-operator/crds/crds.yaml
+kubectl replace -f https://raw.githubusercontent.com/stackabletech/kafka-operator/25.11.0/deploy/helm/kafka-operator/crds/crds.yaml
+kubectl replace -f https://raw.githubusercontent.com/stackabletech/listener-operator/25.11.0/deploy/helm/listener-operator/crds/crds.yaml
+kubectl replace -f https://raw.githubusercontent.com/stackabletech/nifi-operator/25.11.0/deploy/helm/nifi-operator/crds/crds.yaml
+kubectl replace -f https://raw.githubusercontent.com/stackabletech/opa-operator/25.11.0/deploy/helm/opa-operator/crds/crds.yaml
+kubectl replace -f https://raw.githubusercontent.com/stackabletech/spark-k8s-operator/25.11.0/deploy/helm/spark-k8s-operator/crds/crds.yaml
+kubectl replace -f https://raw.githubusercontent.com/stackabletech/superset-operator/25.11.0/deploy/helm/superset-operator/crds/crds.yaml
+kubectl replace -f https://raw.githubusercontent.com/stackabletech/trino-operator/25.11.0/deploy/helm/trino-operator/crds/crds.yaml
+kubectl replace -f https://raw.githubusercontent.com/stackabletech/zookeeper-operator/25.11.0/deploy/helm/zookeeper-operator/crds/crds.yaml
+----
+
+[source]
+----
+customresourcedefinition.apiextensions.k8s.io "airflowclusters.airflow.stackable.tech" replaced
+customresourcedefinition.apiextensions.k8s.io "authenticationclasses.authentication.stackable.tech" replaced
+customresourcedefinition.apiextensions.k8s.io "s3connections.s3.stackable.tech" replaced
+...
+----
+
+Install the `25.11` release
+
+NOTE: `helm repo` subcommands are not supported for OCI registries.
+The operators are installed directly, without adding the Helm Chart repository first.
+
+[source,console]
+----
+helm install --wait airflow-operator oci://oci.stackable.tech/sdp-charts/airflow-operator --version 25.11.0
+helm install --wait commons-operator oci://oci.stackable.tech/sdp-charts/commons-operator --version 25.11.0
+helm install --wait druid-operator oci://oci.stackable.tech/sdp-charts/druid-operator --version 25.11.0
+helm install --wait hbase-operator oci://oci.stackable.tech/sdp-charts/hbase-operator --version 25.11.0
+helm install --wait hdfs-operator oci://oci.stackable.tech/sdp-charts/hdfs-operator --version 25.11.0
+helm install --wait hive-operator oci://oci.stackable.tech/sdp-charts/hive-operator --version 25.11.0
+helm install --wait kafka-operator oci://oci.stackable.tech/sdp-charts/kafka-operator --version 25.11.0
+helm install --wait listener-operator oci://oci.stackable.tech/sdp-charts/listener-operator --version 25.11.0
+helm install --wait nifi-operator oci://oci.stackable.tech/sdp-charts/nifi-operator --version 25.11.0
+helm install --wait opa-operator oci://oci.stackable.tech/sdp-charts/opa-operator --version 25.11.0
+helm install --wait secret-operator oci://oci.stackable.tech/sdp-charts/secret-operator --version 25.11.0
+helm install --wait spark-k8s-operator oci://oci.stackable.tech/sdp-charts/spark-k8s-operator --version 25.11.0
+helm install --wait superset-operator oci://oci.stackable.tech/sdp-charts/superset-operator --version 25.11.0
+helm install --wait trino-operator oci://oci.stackable.tech/sdp-charts/trino-operator --version 25.11.0
+helm install --wait zookeeper-operator oci://oci.stackable.tech/sdp-charts/zookeeper-operator --version 25.11.0
+----
+