Still having problems !!

I have asked this question before, but got a very vague answer. I have a 4s and am trying to change operating systems over to ios7, the response I got was " download I tunes on your laptop, plug in your phone and it will prompt you to upgrade". Well, this is not the case. I have downloaded iTunes , yet no prompt, and when I plug my phone in, it only says that it's not picking up info from my phone. Then states "unable to connect to iTunes". Someone please help !! This has been ongoing now for over a month. Thank you so much !!!