Bilstein has a guide which is pretty informative. You can view that HERE
So, I'm adding some photos and comments to go along with that guide. I think having the photos is a little more confidence inspiring for this. The following is reference the SCHRADER valve shocks. Remote Reservoir shocks will require added steps, but the process is pretty similar.
Tools I used:
-2 large flat head screwdrivers
-small flat head screwdriver
-dead blow hammer
-scrap 1/2" square stock to measure separating piston depth
-Bunch of rags
so, I discharged the shock and removed the core from the valve stem. You may get some oil too.
Then. Instructions say to use a chisel and hammer to separate the cap. You can see the "crack" just below the cap. I used a chisel that had a curved tip that sort-of matched the radius of the shock body. I worked my way around the shock. Don't beat the hell out of it, because it won't penetrate very far. Once the cap is separated a little, use a large flat head screwdriver and work around the shock to get it out.
There are two internal snap rings inside the shock body. One holds the rod guide/seal assembly in. I used a flat-punch and hammer (lightly) to move the rod guide down enough to get the snap ring out. The second snap ring is not far below the rod guide, so, again, try not to beat the hell out of it and I took care not to hit the rod with either the hammer or the chisel.
Theres a "ring" around the top of the rod guide. Use two large flat head screwdrivers to "pry" the rod guide out. Bilstein says you need a special tool for this. I THINK I saw it online for $35. I didn't buy it. Once I got the cap up a ways, I grabbed my channel locks and turned the cap while pushing up. This brought the cap out. Now. Something to be aware of. There is always the possibility that air has gotten PAST the separating piston. If it has, then its now in the main body of the shock. BE AWARE that the trapped air can now blow out. Mine did. If you've ever popped a Pringles can, it sounds like that, but much louder. You won't loose anything, but mine blew out a light film of oil. Nothin critical... but you should always be careful... and have eye protection handy for this step if you're unsure.
Slide the rod guide up the rod. Now you can see and remove the second snap ring. Once its out of the way, slip the rod up and out of the shock body.
Now, just use a suitable container and drain off the oil. The amount will vary obviously on the size of the shock. In my case, i wanted to refer to see how short on oil my shocks were, as that was the problem. My shocks were supposed to have 565ml of oil.... the "bad" one had 425ml of oil in it. Enough to cause it to limit travel, which is the reason I had to break these cherry shocks down. The "good" one had somewhere around 500ml in it.. and it did cycle ok.
Now, with the oil drained, you should remove the separating piston. In my case, I put a rag over the top of the shock body and used a little compressed air to push it up and out. Oil WILL come with it.
Now, this is what you have laying on your bench or floor: