I changed out both 20" Sony TVs in our Marquis. There were 4 screws holding the frame around the front. Get some help to hold the TV while you label the wires. Be sure to label all wires, so you can reconnect to the new TV. Our Bose system uses RCA plugs, so I had to find a LCD TV with RCA sound output jacks. Then measure the space you have, and find one that will allow you to open the doors on cabinets on each side. An overlap of the cabinet frame is OK if you can open all the doors without moving the TV. I bought an articulating arm to mount the new TV to the side of the cabinet inside. This allows the new TV to be positioned facing any direction within reason and tilt down. I found the 26" LG fit without cabinet work. The manufacturers change models and sizes frequently, so you need to shop for one that is available that fits the space. We also bought a Vizio for the bedroom. We like the LG better. Now there are LED screens available which are thinner, and take less space. I would look for one of those now. It is a good project. Have fun.
Larry