Have iPhone 4S but can't update iOS 6?

When I go to settings, general, software update… Download and install button is not highlighted so I can't download it. A number one is attached to the setting app saying I have to update my software but can't push the "download and install" what to do?

Maybe you don't have enough memory? I just got mine and it came with iOS6

You may not have enought memory. Check your phone to see how much memory you have. If you have enough, Connect it to ITunes and try to update it manually. If that doesn't work, then call the support number for Apple.

Also, power your phone completely off then turn back on. I had to do that.