You don't. iOS 5.0 is permanent. Hence why the betas, if you had cared to do your research, warn against using them on a device that isn't entirely meant for testing.
Why? Because it's painfully obvious that every idiot and his brother try to use beta software meant for developers without knowing what they're doing? Then they come on here and beg for help for a problem they caused because they felt like doing something stupid.
If you feel like being the one to help the people that went and illegally downloaded iOS 5 and are having problems because of it, be my guest. But I'm not about to be the one who's enabling their stupidity.