Here are some links on how to remove the ECU, followed by some descriptions on the A3 ECU removal..
http://forums.tdiclub.com/NonCGI/Forum4/HTML/001435.html http://forums.tdiclub.com/NonCGI/Forum4/HTML/001799.html
A3 ECU removal.
Remove the plastic cowling at the rear of the engine compartment under the passenger wiper blade. there are 4 screws retaining it, the first one on the far left is a screw , the other 3 are screws set into square retaining clips, unscrew them 7 or 8 turns and then use a pair of pliers to grasp the screw head and wiggle backand forth turning and pulling . the retainer comes out withthe c=screw, they can be a pain to get out.
Remove the cowling on that side and you will see the ECU, there is a 10 MM bolt and a nut holding it in place, remove the bolt loosen the nut.
There is a boost sense hose going to the ECU with a pinch clamp on it , pinch the clamp and slide it down, then pull the hose off.
The electrical connector is a zero insertion force type. it has a slide release on the end, slide the release towards the boost sense nipple untl it almost touches it, the connector will come off easily when the slide is released.
Remove the ECU, Use a T10 Torx screwdriver to remove the 4 torx screws on the end of the ECU. Use a philips screwdriver to release the ECU from it's bracket. Note the orientation of the bracket to the ECU and which side the boost nipple is on so that it can be put back in as it was, it will not harm anything to do it backwards, but may key VW into thinkuing that the ECU was tampered with if not put back in as original.
Use a flat screwdriver to seperate the end of the ECU from it's case. When you clear the case you can remove the board, place the ECU board in front of you so that the connector is facing away from you.
You will see two small square chipsi n socekts on the left hand side of the board, there are tags on them that are numbered, the highest numbered chip always goes into the left socket.
Observe the chips that are in the ECU, they have a small indentation indicating pin 1 on the lower center of the chips, when you install the new chips you want to be sure that this notch is orientated properly.
Use the extraction tool to remove the OEM chips, make sure you are not on carpet, tile or linoleum is preferable as static will damage the chips. If you look at the sockets you will see that the lower left corner and upper right corner has a space to put the extractor blade into. seat it as far as it will go and squeeze the handle, the chip should come out of the socket evenly and with little effort, orientate the new chip and insert it gently into the socket. Now do the next one. If you wish you can remove the OEM chips lables and exchange them for the upgrade lables, do one at a time so that they do not get mixed up. use a razor bleade to lift the labels off. It is not absolutely neccessary but will prevent the neccesity of removing the chips when you take the car in for servicing.