One, wrong forums, you'll get no help here if the question is aimed at any other CoD
Two, you use a prestige token to reset BO2 stats back to starting default (also re-locks everything, and I mean everything) - if you don't have one of those pretty prestige tokens, start a whole new xbox live account cause there isn't any other way...
Three, you're welcome because I actually answered your question even if it was completely in the wrong place... lol
I have moved your post to our Black Ops 2 Tech Support Forums.
Once you hit Master Prestige you will not be able to use any tokens to reset your stats. For more information on this please check out our Activision Support knowledge base article!