Reversed (or previously applied) patch detected

Continuing the discussion from How to upgrade in a noob language:

This message indicates that a part of the upgrade appears to have been already completed beforehand. This usually occurs when someone has manually applied a patch to fix a bug in the old version. The new version will contain the same fix(es). You probably want to select “n”: no, do not reverse the previously applied changes.

In the broader picture, however, patch-based upgrading is discouraged.

If you are maintaining local code changes, best practices demand the use of version control (such as git, subversion, or similar) and version control can manage the upgrade changes.

If you are not maintaining local code changes, the best practice is to use the “Full Package” upgrade. This avoids all of the pittfalls of the patch command.