Backing up scenery files?

[ETaylor]

Hello, I know this may be a stupid question, but I do not know how to backup my stock scenery files. I'd like to do this so I can download some new files, and if I don't like them, revert back to the stock files.
I imagine it is a simple prcedure, maybe just making copies of the files? Question is, wihch files?

Thanks for the help.