Do I wait for iPhone 5 or keep iPhone 4?

I use at&t's go phone service for my iPhone 4 because I'm 14 and that's what I can afford but im sure it's getting close for The iPhone 5 release so I need money to buy it unlocked. Should I sell my iPhone 4 now and wait for the iPhone 5? Because if I sell it after the release it'll be a reduced price compared to if I sell it now. Or should I just keep it just incase? I don't know what to do. Advice?