I'm assuming the new seats are from a 1998-2004 Blazer, Jimmy, or 98-01 Bravada, Envoy...or else you will have issues with bolts lining up and power supply.
First thing, is check that you can remove the T-50 Torx in the inner rear of the seats. You may have to perform the drill trick to move the power seats up enough to get to it. (youtube has some good vids)
I've run across many a good seats, but alas, could not budge those wretched torx bolts!
Use a good breaker bar, WD-40 or similar, and maybe a hammer/mallet to help break the loctite on the threads. My local salvage yard doesn't allow torches, car batteries, or anything fun that would help...hopefully yours does?
If you can get those out, you should be golden. The other three bolts come out easy with a box wrench. Just use a flat head screwdriver to pop up the little black cone trim pieces. There will be a thin, round metal piece on the bolt sometimes...thats for the trim to stick onto (or its still inside the trim). Try to keep those, or just use your old ones.
Also, if you don't have power seats currently, fish around under your carpet...should have both plugs taped down under there, on the appropriate sides.
It is a T50, I know because I broke my T50 bit at the junk yard trying to get a seat out so that I could grab the female end of the seat belt. There are 3 15mm nuts (maybe 14, I forget) and 1 torx bolt. Take a look at the picture, you can see that it is a T50.