Hi Paul, If you want to fit limiters to your shocks you will need to do the following:
Remove the shock spring 1st, then unscrew the cap off the top of the shock and drain the oil out.
Next you will need to unscrew the lower shock mount from the shock shaft (the piece that connects the shock to the wishbone). Do this by gripping the shock shaft with a pair of pliers, make sure you put a piece of rag around the shock shaft to stop the pliers from damaging it and unscrewing it anti-clockwise.
Then unscrew the lower part of the shock body, you don't need to do this part but will make it alot easier to refit the shock shaft. You can now remove the shock shaft through the top of the shock body.
There will be a couple of O rings and a spacer in the bottom of the shock body where you just unscrewed the lower part, hook these out remembering the order you removed them. Should be O ring, spacer, O ring.
Once you have the shock shaft in your hand slid a spacer or piece of fuel pipe onto (over) the shaft ( I use 10mm spacers).
Then re-assemble everything in the reverse order, with the spacer inside the shock body. This will then reduce the downward travel of the shock by what ever length of spacer you fitted.
Re-fill the shock with silicon shock oil, the viscosity is up to you, but anywhere between 30-50wt (300-500cst) should be fine for normal use.
Bob's your uncle & fanny's your aunt, and your done.