It depends a little on which type of Rollei TLR you have. The earlier ones are referred to as having a non-removable screen, and then, of course, the newer ones are referred to as having a removable screen. The main issue here is the size of the screen, as they are different. Hence you need to make sure what type you have when you order a screen.
I have a 1953 Automat MX, a model with a 'non-removable screen.' It is still removeable. You do so by undoing the 4 screws that hold the viewing hood in. Once unscrewed, the viewing hood comes off along with the screen. You could then clean the screen and replace it. Be very careful not to damage the first surface mirror in the body, this is the mirror that bounces the image from the viewing lens onto the viewing screen. While it might have dust on, it is extremely delicate, and I recommend that you leave it alone.
About 12 to 13 years ago I replaced the very dark original screen with a Beattie Intesnscreen plus, which was a big improvement. The focus, though, had to be adjusted after I put in the new screen, so make sure to check this out. I've heard that Marflex (offical USA Rollei repair shop) will put Rollei's new bright screen into a TLR, but you'd have to call them to be sure. Another option would be to use Bill Maxwell's screens. I have on for my 4x5 and I love it.
-Peter
