Jailbreak Problems (unjailbreak)?

Ok, so I have an iPhone 4S, running iOS 6.1.1 and I'm wanting to unjailbreak due to iOS 7 and the fact that I'm selling this phone potentially. But, every time I try it on my computer I get error messages and then I fix that error and it jumps to another and another and so on. So then I tried updating it from my phone to the new update but when I try to do that it never loads the update it just sits there saying checking for update. I let it sit all night and it said the next morning same thing. But the thing is I can download the update on a computer but when I try to put it on the device it pops up with error messages. I'm getting very irritated trying to update to the latest iOS 6.1.4 I believe. So if anyone could help me it'd be very appreciated. Side note I have tried other computers. But not my grandfathers. But I have an iPhone 4S running iOS 6.1.1 and I'd like to know how to unjailbreak. Thanks! If anyone would like to text me and help feel free 806-663-0775

Force recovery mode http://support.apple.com/.../kb/HT1808. If this doesn't work you're f*cked.

You need to register your device's UDID with a developer account through a site like http://www.udid.in/ for $5, since you installed unreleased software.