1) From the driver's wheelarch, lock out the aux belt: 15mm spanner on the tensioner, lock it out with a nail or similar
2) Remove belt.
3) The PAS pump is above the air con pump. There are two banjo bolts attaching the PAS pipes to the pump, undo these, they have two copper washers each. Fluid everywhere, have a bucket handy.
4) Undo the bolts going front to back on the PAS pump - 13mm I recall, quite long.
5) Remove and replace pump.
Pretty simple, but access is limited. Remember to refill with fluid, the system is self priming.