In mine it is Settings/Back up and Reset. Obviously back your stuff up to something - mine is Samsung so I can use the clunk old Kies for a back up. Painful, but worth it. Then reset to factory settings.
Then, be very careful when you set up the phone from "new".
The big "but" is that Google just loves ferkin adverts, so might still sneak them in. Google, Apple and Farcebook appear to be in a race to "monetise" mobile things, and appear to me to take no prisoners.