How do I know if I get CPU?

I'm a little confused about the upgrade process. I've been Googling, and turned up that it's done in "sweeps", and there are problems, etc. But... if I do get it, how do I know? On the waitlist for my flight, they show 15 pax in first, but none on "standby". I thought I'd show up there, and others as well.

Also, what's the story with RPU/GPU? I gather they come at certain miles. How do you know if you have one, and how do you use one?