easy mate to be honest. I was going to do my self but i didnt have a deep enough socket to get the internals from the inside of the pump, so i just paid £50 bucks to get it fitted,
some people say yuo need to set the car to top dead centre before you do it, but when i had my fuel pump replaced under warrantee a couple years ago when it went tits up, they never did that, and when AMD fitted my internals i dont think they did either.
Ill have a search around, there is a good how to guide from mater somewhere. ill post a link