How to revert my ios7 iphone back to ios6?

I have completely messed up my iphone 4,
i've had ios7 on it for ages now and everything was fine but last night it randomly turned off and when i turned it back on its come up with choose a wifi network, i cannot get off this screen and get back to menu or do anything with it,
does anyone know what i should do from here as i need my phone asap
any real help is much appreciated, thank you

Restore it on iTunes.