It's covered in the Bentley under Brakes I believe.
If you're talking about the rotary-style pump, you just remove all the slotted screws, install the new diaphragm, and then PRE-TENSION the diaphragm, and install all the screws again. Bentley says to remove the circlip from the piston, leave the diaphragm loose, etc. If you do it that way, you'll be rebuilding it again in under 10k. Just pretension the diaphragm and you'll be fine.