Unlocking iPhone 4 for costumization reason.?

I have the iPhone 4 & I love it, but I wanna be able to costumize it like I wanna & I'm getting the IPhone 5 as soon as it comes out. so I figured I could unlock it until I get the iPhone 5. how do I do it on Windows 7 & how do I get the stuff to costumize it ? thanks:)