You could go to the settings menu then to picture. It should have a mode or size category. I doubt that your aspect ratio is off so you shouldn't adjust that setting. Also. The newer HD TV's have built in memory's for each cable port. So, if you changed what ever was plugged into the port you are using now, that would explain the changed picture size. You can usually go to the manufacturer web site and download a free cy of the user manual. He this solves you're problems.