I know that REP are inactive on exchanges. How do I activate and deactivate my REP tokens once in my own wallet?
I can see from these questions that we need to do a better job of communicating the changes to the reporting system! As Micah's comment says, we've gotten rid of the notions of dormant/active REP, and replaced it with an opt-in system per reporting window. (See this answer for details.)
I suspect your follow-up question would be, "How do I opt-in to report during a particular reporting window?" The answer is that you'll click an "Opt-in" button in the UI and, Bam! You've opted-in to report during the next reporting window. Just remember to actually submit reports during the upcoming window, since after you opt-in, you're committed!
REP tokens are supposedly not "in-use" / "active" when on centralized exchanges, however there's no way to be sure. If you want to make sure your REP tokens are not used on the platform, simply store them in a wallet where you are the sole owner of the private key, ideally offline for best security.