How to download iOS 7 for my iPhone 4s?

I would like to get iOS 7 for my iPhone 4s but i don't know what website to download it on. Everytime I follow the instructions something seems to not work at the end. Can anyone help me or tell me an easy way to do it please?

Well, the first way is to pay $99 through Apple's Developer Site, but not everyone wants to pay that much lol!

Another way (which I've done myself, so it works), is to go to a UDID activation website like http://activatemyiphone.co.uk/ - I did this for my iPhone 5 and my iPad 3 and my UDID's were registered straight away. These guys provide you with technical support, so if you have any problems, you can email them and they'll fix it with you.

You need to register your device's UDID on a site like http://www.instantudid.com/.It's $5, and they literally registered my UDID instantly. Then I was able to download iOS 7 from imzdl.com and install it.