How can I get back the iOS 5.1.1 software in my iPhone 4

I just get the new update in my iPhone4 but it's a screw change systems if you company knows that news programs can be used in olds cellphones no matters if are you products so let's thinks more and how makes changes all the time and put advert to People who's dosent know if the olds cells gonna works with the newrs programs made by you same seller company buy the way thanks for just ruin my 3 months cuz I can sent pictures I videos to my family thanks to you renovations of programs!!!