How do I re-install 10.1.1 or 10.1.2? Because 10.1.3 is constantly crashing and I can't wait for the fix.

I upgraded to 10.1.3 last week and have had nothing but problems. The program crashes continually for a variety of reasons, and while I can eventually get it up and running again, I can't isolate the causes of the crashes. I would like to "revert" to 10.1.2 or 10.1.1. How do I do this? ( I don't have the old program saved).

I have been using FCPX since it came out and FCP (the original) since it was introduced. Thanks, John Feldman, Hummingbird Films