How to replace tail light on VW golf mk5 estate

Although you posted this question under a 03 VW Golf and you have a MKV. The best I can do is a MKIV set up. From the rear trunk there are access ports just for this job. The right port will be just above the light housing you will find a wire harness for the right assembly. Follow the harness and it will lead you to the assembly. Once located you can squeeze the two tabs and pull the circuit board where the bulbs are installed. Push on the bulb and twist anti-clockwise then pull out of the socket.

The left should be the same procedure and it is located behind your audio components.

NOTE: It's a good idea to wipe your hand and the glass bulb, leaving oily residue will cause early bulb failure once in operation.