Articles and Article Categories can be renamed from their edit screens.
If you need to rename a Snippet Type that's in-use in its Category, you need to duplicate the Category, do your fixes in the duplicate, use the options menu (F7) for the Category to move all of the Articles to the new Category, then delete the old one. (Alternatively, duplicate, move everything, change the original, move everything back, delete the temp one.)
Also, this is the forum for tutorials and videos. Questions should go in the
Discussions forum.