To the best of my knowledge, this page accurately describes the procedure that I followed to change the sparkplugs on my 2000 A4 1.8TQ. Although all 1.8T engines follow a similar configuration, I cannot confirm that this procedure will work for your car.
Use these instructions at your own risk.

• 5mm hex key socket attachment.
• 16mm (5/8") sparkplug socket.
• Socket wrench with 6" extension.
• Sparkplug gap gauge with electrode adjustment tool.
• Torque wrench for tightening sparkplugs.
• Flathead screwdriver for removing engine cover.
• 4 sparkplugs.
• 1oz. anti-seize compound.

 

1. Remove the engine cover.

Loosen the 3 plastic screws using a flathead screwdriver and pull straight up on the cover to remove it. Engine cover screws (yellow arrows)

2. Detach the wiring harness.

Coil harness (image from Bentley Publishers) Unplug the wiring harness from each of the coils.

3. Remove the coils.

Coil bolts (yellow arrows) Loosen the 8 coil bolts using a 5mm hex key and pull the coils out of the engine.

4. Replace sparkplugs.

Cylinder 1 Check the gapping on each plug and adjust to the recommended gap. NGK recommends a 0.028 gap for the 1.8T engine with the ATW engine code, but anything in the range 0.028 - 0.035 should be fine. Use the 16mm sparkplug attachment and 6" extension to remove and replace each sparkplug. Optional: apply a light coat of anti-seize on the threads of each new plug. Use a torque wrench to tighten each plug to 22ftlb. Do not overtighten or else you will damage the aluminum cylinder head! NGK PFR6Q Laser Platinum

5. Reinstall coils, wiring harness, and engine cover.

New vs. Original factory plug after 51,409km The Bentley manual recommends tighttening the coil bolts to 7ftlbs (thanks for the info Art!).