Q: my t-mobile iphone 5 does not have the software update for ios 7 Why?

Why does my iphone 5 have no available update and its still running on ios 6.**. I have t-mobile and the phone still has a lot of memory. Also the phone was purchased directly from tmobile and its only 3 months old. THis is the whole reason why i bought the phone in the first place. I want ios 7!!