How do I update mmy jailbroken iPhone 4?

I've been wanting to update to iOS 7 since forever, but due to my stupid decision to jailbreak it a while ago I can't. I've tried going to software update, but I've left it searching for hours and all night, and it never finds it. THEN just my luck iTunes refuses to open on my laptop at all, so I can't even restore it. Please help, I've learned my lesson about jailbreaking the hard way, but I'm seriously the only one who still on iOS 6.