Improve upgrade instructions (#3509)

* Rename KServe models web app and update README

Updated README to reflect renaming of KServe models web application and provided deletion instructions for old resources.

Signed-off-by: Julius von Kohout <45896133+juliusvonkohout@users.noreply.github.com>

* Potential fix for pull request finding

Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>
Signed-off-by: Julius von Kohout <45896133+juliusvonkohout@users.noreply.github.com>

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Signed-off-by: Julius von Kohout <45896133+juliusvonkohout@users.noreply.github.com>
Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>

Author: juliusvonkohout

README.md

@@ -635,6 +635,19 @@ The following manual steps are required when upgrading from `release-26.03` to t
    The hashed `ConfigMap` resources (`namespace-labels-data-*`, `profiles-config-*`) are recreated under new hashes by the new manifests and can be left untouched.
    > **WARNING:** Never delete the `Profiles` CRD; it would delete every profile namespace.
 
+4. **KServe Models Web Application**:
+   ```sh
+   # Legacy KServe Models Web Application (renamed from kserve-models-web-app to
+   # kserve-models-web-application). The old misnamed stack is no longer in the
+   # manifests, keeps the unbound kserve-models-web-app ServiceAccount, and still
+   # claims the /kserve-endpoints route, which causes RBAC 403s on SubjectAccessReview requests.
+   kubectl delete -n kubeflow --ignore-not-found \
+     serviceaccount/kserve-models-web-app \
+     service/kserve-models-web-app \
+     deployment/kserve-models-web-app \
+     virtualservice.networking.istio.io/kserve-models-web-app
+   ```
+
 ## Release Process
 
 [Kubeflow release handbook](https://github.com/kubeflow/community-distribution/blob/master/releases/kubeflow-ai-reference-platform-release-handbook.md).