Disassembly:

1. Jack up car, place jack stands under chassis
2. Remove the wheels
3. Using open ended wrench to hold guide head pin, remove the bolts which hold the caliper to the mounting bracket
4. Remove the caliper then remove the pads
5. Remove some brake fluid from the reservoir then use a big c-clamp to push the pistons back into the caliper. Be careful not to damage any rubber parts. For the rear brakes, the piston has to be screwed back in. The Bentley manual says that a hex key is used, but most (all?) seem to require a special tool that has two small projections to mate with two indentions on the piston. The official Audi tool is pictured below left, but it is expensive (~$85 from Zelenda tools, 1-888-892-8348). An equivalent tool designed to be used with a ratchet is available at most auto parts places for $10 to $15. A common one is called a Disc Brake Piston Tool  (P/N 28600) made by Lisle, (28300 & 25110 are obsolete Lisle P/Ns that should also work if you find them on the shelf). A similar cube tool is available from KD tools (P/N 3163 pictured below right). These little cubes have various fittings on each face for different cars. The only disadvantage to using a cube tool is that you have to simultaneously apply inward pressure on the piston as you turn it while the official tool does both for you when you turn the knob.
   

   Official Tool

   Lisle 28600, 28300, or 25110

   KD Tools 3163

    

6. If you're replacing the rotors, or turning them, remove the caliper mounting bracket so that the rotors will come off.
7. Replace any rubber parts that look doubtful

Reassembly:

1. Place rotor back onto hub. (You can use a spare M14x1.5 bolt to hold the rotor in place.)
2. Bolt caliper mounting bracket back onto hub, using locktite or new bolts.
3. Place new pads into caliper with the blue antisqueal gook between the pad and the caliper to prevent squeal. This will prevent the brakes from squealing, maybe. A whole bunch of RTV supposedly works better. You want to really deaden that vibration mode and too much doesn't hurt.
4. Place caliper into caliper mounting bracket very carefully, so as not to damage the rubber parts (either the old ones, or the new ones you just replaced).
5. Replace bolts which anchor caliper to bracket, with lots of grease in the rubber slide. Make sure rubber parts are properly engaged in mounting bracket and caliper bolts.
6. Tighten caliper mounting bracket bolts, and caliper bolts per Bentley's torque suggestions (or just reef on them as hard as you reasonably can with a 3/8" ratchet.) (That means "no hernias") This is the time to bleed the brakes if that is your desire. (See below) If not, just make sure the reservoir is full.
7. Replace wheel, wheel bolts, and torque to taste. (Don't forget to remove the little bolt that was holding the rotor on the hub if you did that in reassembly step #1.)
8. Remove stands, lower car, and check brakes. Test drive and bed in pads per manufacturer's directions.