Have you tried different routers? Some particular routers, have compatibility issues with the iPhone, so you might want to try a different Wi-Fi network to see if it works. Also, like the previous user said if your iPhone, is jailbroken, you cannnot update it - unless, it's a jailbroken version itself. Try resetting your network settings again, and see if it helps out. The other option would be resetting your iPhone all together - and possibly, doing a fresh install.