Right, here it is : This information applies to my Polo but I am sure the layout is very similar.
The stop-light switch is mounted on the pedal bracket below the fascia.) You may have to remove some trim to gain access)
Reach up behind fascia and disconnect wiring connector from switch.
Twist switch through 90 degrees clockwise and realease it from the mounting bracket.
Prior to refitting replacement switch you should fully extend the stop-light switch punger.
Fully depress and hold the brake pedal, then manoeuvre the switch into position. Secure the switch in position by twisting it through 90 degrees anti-clockwise, and release the brake pedal.
Reconnect the wiring connector and check the operation of the stop lights. The brake lights should illuminate after the pedal has travelled about 5mm.
Replace trim.
All this is from the Haynes manual. Sounds a bit fiddley, but good luck !