I can appreciate your apprehension stu aull. I also used a whole new set of DVD’s when I installed vers 5.1 from 5.0.3. When you get to the screen in the install process where you actually have to hit the “install” button it should actually say “upgrade”. also if you look at the version numbers on the disc you will find that some are the same version. (although you should use the new discs only when you upgrade to 5.1)
If youre still not sure, what I’ve done is hit command f to do a find and just delete everything that is associated with the FCP studio. (It’s probably not the best way but will work if your careful.)
I still think that if you use the new set and just go ahead and install all the files will be replaced in your application folder. Macs are good that way.