How to switch between multiple files in UNIX while using VI editor?

For Linux Red-Hat VI version 7.2.411 use :n and :N to switch next and previous.

Next file: :n

Previous file: :p, :N or :prev depending on which vi implementation you're using.

Here's a typical cheat sheet which has a section "Files" on this topic.

http://www.lagmonster.org/docs/vi2.html