Well, first you grab your wrench (I think it's a 13 or 15mm... not sure) and unbolt <scribble> snap off the heads of the bolts holding the original bumpstop on.
Then you bolt the new one on <scribble> curse a lot, grab the angle grinder, clean the rust and undercoating off the bottom of the frame rail, clean the excess rubber off the mounting tabs of the new bumpstop, and tack weld them in place.
Oh, the front is way easier. I've never actually bothered, but the rubber part comes out of the socket and iirc on some years the socket unscrews with a big pipe wrench.
I used a small bottle jack and a block of 4x4 to push my stops in. Although I had no springs on at the time. Be careful doing that as it can come flying at you if you are not squared off.