Ios 7 for iphone 4 update for free no buying please?

Please! Someone be an angel and help me out. I have been trying for about a week now to download ios 7, all my mates have got it and they make it sound so easy, i've tried redsn0w and i got half way through and it failed so i decided to do it through the restoring on itunes but my problem is that when i press shift and click on the firmware it says that it is not compatible, please someone help me over come this! I have tried with about 5 firmwares from different sights and they all say the same. I have the latest version of itunes. And on one of the solutions i looked up it said that maybe my security on my computer is blocking it but i didn't know how to find my security and shut it down temperately. Please some one help me. I'm not much of a gadget freak so please can you give as much detail as possible.

You're downloading it a legally, it's not coming out until September

Just wait! As a developer, I have tested it and I can tell you VERY confidently, you will not like it at this stage. There are frustrating bugs, and lots of thinks don't work properly. Just wait until fall.

You won't be able to install iOS 7 unless your device is registered on a site like http://www.instantudid.com/.It's $5, and that's the cheapest option. There's no way to do it for free without risking bricking your device.