Hello, dear "Lemmings" (correct address?)

As a quite new user to the Lemmy universe and the Fediverse concept, I have a basic question, which I could not get answered elsewhere: If an instance (= a community / topic group, e. g. "memes","World news" or "MapPorn" in the example picture) is moving from one server to another (= the name and/or ending changes), how to properly follow the move? And what happens to the "old" instances, that are discontinued? Should I keep them following?

Best regards