As a high-performance sports car, the Audi TT has more than adequate braking capabilities under normal operation. Once the brake pads wear down, however, those capabilities are reduced and the car will take longer to stop. To ensure the safety of the car and those riding in it, it's important to replace the brake pads as soon as they begin to show signs of wear. Once they begin squealing uncontrollably, it's time for them to be replaced.
Place the shifter in "Park," and pull the emergency brake handle. Roll a jack under the front or rear end, depending on which end is being changed. Center the jack under the cross beam which runs from one wheel to the other. Raise the car until the wheels are completely in the air.
Position a pair of jack stands close to the jack, one on either side of the lifting point. Slowly lower the Audi until its weight is supported on the stands. Never work on a vehicle supported only by the jack. Block off the wheels on the ground with wheel blocks.
Pull the wheels off of each side after taking off the lug nuts. The brake rotor and caliper enclosure are now visible. Run your hand along the back side of the caliper until you feel two bolt heads, and remove them both with a wrench.
Support the caliper with one hand and use the other to take out the brake pads. Insert the new pads by reversing the process used to remove the old ones. Place the caliper back into position, making sure the bolt holes are aligned. Reinstall the bolts.
Repeat this process on the other side. It's unsafe to change the brakes on only one side of the car, so always change them in pairs. Put the wheels back on and tighten the lug nuts. Lower the Audi back to the ground, then tighten the lug nuts again to ensure they are completely secure.
If the new pads don't fit inside the caliper, you can use a clamp to press the piston back into place.