rite well this should be a walk in the park to you.
get the car jacked up and remove the wheel.
1. look at the calliper and you will see there are two ridged rubbers with bolts (i think they are 12mm) sticking out of them. there is one at the top of the calliper, and one at the bottom. Remove both of these.
2. Having done that, remove the calliper (the bit you have just slackened by taking the bolts out) away from the pad carrier. a large flat blade screw driver can be handy to lever it off with. be careful not to lever against the surface of the disk though.
3. the pads will fall out when you do this.
4. Clean up the surface of the brake pads with a bit of emery (spelling) cloth, and the 4 flat surfaces on the pad carrier where the pad sits and slides. use a wire brush on the pad slides if you wish, to ensure they are properly clean. You can remove the pad carrier to do this if you want (this is done by removing the two large bolts that secure it to the hub - the only two bolts behind the disk).
5. grease the flat surfaces of the pad carrier where the pads will slide with alu-grease or normal coppoer grease (available from halfords)
6. Replace the pad carrier (if you removed it) and replace the pads into the slides.
7. Replace the calliper in the same way as you removed it, ensuring that that the castlations on the pistion are lined up with the knuckle on th back of the brake pad. so long as you havent wound the piston back (which you shouldnt really need to do to be honest) everything should be fine, as it will still be lined up from when you removed it.
(if you are putting new pads on however you will need a piston windback tool (available from halfords), as unlike front brake callipers the piston must be wound back in a clockwise direction, not pushed. you will have to do this with new pads as they will be wider than the ones you have removed , and so the piston needs to be pushed in a little to allow them to fit and then lined up.
8. replace the bolts into the rubbers and tighten them WITH A SPANNER, as they do not ned to be overly tight,
9. put the wheel back on!
job done.
on reading this i realise that it seems fairly complicated. but it really isnt when you actually have a look. its pretty straightforward. any Q's, fire away.
hope this garbled description was of some help.
stuart