Welcome to IRV2.
We just replaced both tv's in our 2006 Tiffin Allegro Open Road.
The front tv has 2 (4") screws in the cabinets on each side of the tv. Remove these screws and then you can remove the frame around the front of the tv. We had to use a putty knife along the top edge to loosen the frame from the ceiling fabric.
After you remove the frame there are wooden blocks held by screws holding the tv into the cabinet. Remove the screws and the blocks should slip out. Be careful when you pull the tv out of the cabinet and have somebody handy to remove the plugins from the back.
Join the Tiffin RV Network and do a search and you will find more instructions and pictures of how other Tiffin owners have replaced their tvs.
Tiffin RV Network
Jon