How to install ios 7 on iphone 4s?

I really don't have an idea of this stuff so i came here to ask for help because i really like the update. I have an iphone 4s 6.1.3 and i'd be so happy if upgrading my ios 6 to 7 is possible. I tried searching on how to do it but i always get stucked on where i will click the 'Check for update' on itunes. It says "this version of the iphone software is the (6.1.3) current version". I can't pick a version. I'm really confused til now. In the video tutorials, somethings showing up after clicking the 'check for update' and its the (for the choosing an update) but for me its the "this version of the iphone software is the (6.1.3) current version" is showing not the choose a version (something like that).

P.S. Pardon my english. Please help. Want this update so bad. All answers will be much appreciated! Will really make my day.

That's because iOS 7 won't be released to the public until the fall, but you can install it early if you register your device's UDID with a developer account through a site like http://www.udid.in/.It's $5, and then you can try out the new OS before everyone else. That's how I got it on my 4S.