How do I upgrade from 4.3.3 to ioS 5 and above?

I am going insane trying to figure this out. When I attempt to upgrade through iTunes I keep receiving this message: "Make sure your network settings are current and your network connection is active." When I originally purchased the iPad I purchased a network for $30 a month but now I just use my home wireless. Does this have something to do with it?? HELP!