Shock rebuild is pretty simple. Bleed out all the nitrogen from the bladder. Remove the shock spring. Take some penetrating oil and spray the reservoir end cap and push it in a little ways until you see the spring retaining clip. Hose it good with. Compressed air and a brass soft bristle brush to clean any dirt. Remove the clip carefully so as you don't create any burrs. Now you have to remove the end cap. Lubricate it good  and push in the shock shaft, this may pop the cap out. If not you can use a little compressed air to get it out. Turn the pressure way down or use a bike pump. Hold a rag over the end as it will want to launch out along with oil if you give it too much pressure .
With the ressie disassembled, move to the shock body, use a chisel carefully , to get the bottom out cap to loosen up its a press fit. With the cap removed use a clothes pin to hold it up out of the way.  Clean this cavity good like you did with the ressie cap. Now the hard part, you need a piece of pipe about 2 inches long that will fit over the raised seal on the seal head.   Cut a slot in the side and slip it over the shaft, remove the clothespin and push the shaft down to engage the pipe. Press on it to depress the seal head exposing the retaining clip. If it won't budge usually a tap or two with a soft face dead blow will dislodge it.  Remove the clip carefully. I like to use dental picks for this. Once the clip is out re-lubricate and put shock spring back on, slowly tighten and draw the shaft and seal head out.

Once disassemble Clean everything pristinly. You have to grind or drill off a small amount of the shock shaft off to remove the retaining nut . Once off be careful to not lose any valving I use a zip tie to slide it on to then  close it . The seal head will slide rite off but you need a bullet to replace the new one onto the shaft to not ding a seal.  Now is a good time if you want better valving to replace the valve with a race tech gold valve or a stadium suspension systems valve and Ohlins style shim stack.