Coming out of the Friend Zone is about as easy as coming out of the Dead Zone. The Friend Zone is the Point of No Return.
It's like saying "How can I get a girl to like me after she has officially told all her friends that she would never like me?"
As Carlos Xuma said, you are (at least) 10 times more likely to find a new girl than resurrect one who has already determined you are not good enough for her.
But if you insist, you must improve yourself physically enough to wow her. Carlos said it best: "Why would she go back to something she has already said she didn't want unless you improved?" Start with a 3 day fast and liver cleanse.
Guys, when you get it right (and trust me, it took me 25 years), you'll have so many options that you won't have time to sulk over one girl. You'll also notice a funny phenomenon: the girl you saw last is the hottest (the contrapositive to the out-of-sight, out-of-mind phenomenon that holds us back).