How do I make my Samsung TV to be full screen?

I set have a Samsung Flat Screen Television and I have already changed my screen ratio to 16:9 already but it's still not full screen. The left and right sides of my screen are black. When I bought my television you could watch TV in full screen but I think it got changed by accident.How do I make my Samsung TV to be full screen?most TV's I know use the # key on the remote to cycle between viewing modes. Try that on your Sammy.