I recently rebuild the calipers on my '83 Esprit. The process is fairly simple, but will take a couple hours to complete. The rebuild kit consists of 4 rubber seals, 4 rubber dust shields and 4 retaining rings.
Now the workshop manual says that you should blow the pistons out with compressed air, which I did. The problem is that the calipers are dual piston, and compressed air only blows out one of the pistons. If you have a frozen or slow caliper, that is the one that is going to be stuck in the caliper.
If I had it to do over again, I would build/buy a fitting that would allow me to attach the compressed air nozzle to the caliper (I only had a standard valve stem connector that I held to the opening by hand.) I would also build some kind of a device that would fit in the caliper that would prevent either piston from coming totally out of the caliper so that the compressed air forces both pistons out most of the way.
What I did do (and you could probably do if you didn't have access to an air compresser,) is to place the caliper in a vice and with two large flat headed screw drivers I gently pried the piston out of the caliper.
One thing to note (because it isn't described in the workshop manual,) is if there is a key in the piston. If the piston is keyed, make sure you mark/remember which way the key faces. This is important to the operation of the braking system, and installing incorrectly will affect braking.
I used a small flat headed screwdriver and gently pushed the head of the screwdriver between the rubber seal and the metal of the caliper.
Use emery cloth or fine steel wool to clean the pistons and calipers, make sure you remove any dirt and debris from these areas and keep them as clean as possible (I blew out the area with compressed air after cleaning, then used brake fluid and a clean rag to wipe out the area.)
I found that the seals have the tendency to twist when pushing them into place, make sure you're working in a well lit area and inspect each seal to make sure it's not twisted .
This is by far one of the more time consuming processes. It is impossible to get the pistons perfectly lined up. I applied generous amounts of brake fluid to the lip and interior of the caliper and the outside of the piston. Then I would fit the piston into the caliper trying to keep it as straight as possible (remember which way the key sits.) The piston will bind on one side. You should be able to get an idea of what side is binding (it's subtle, but the piston will be tilted slightly.) I then took a large adjustable plier and applied pressure to the high side. This is a judgmental application of force. Too much and you can scar the piston or worse, the caliper. You should end up in a situation where you “wiggle” the piston by applying pressure to each side back and forth until it's in the caliper about 1/2 way. Then I was able to push the piston in by hand.
This is just a pain in the butt activity. Slipping the dust shields on is easy enough, but the snap ring is a pain to get it positioned.