Clubby is correct.
Collar spins up/down to preload spring, spin it back, spring loosens.
When this happens, be prepared, bike gets slack.
Remove bolts either side of damper, voila, removed from bike.
( I like to use a piece of pvc pipe, drill holes holes in appx spots, and install in place of shock with just the bolts, otherwise it gets all noodley)
Clean everything up, measure length of shock sitting, and length compressed.
Take lots of pictures of shock.
We will go from there.
This is my DH Big Hit FSR went Fox shock puked it guts @ AngelFire. Pretty much same setup.