Changing the right side one on a US car is pretty straightforward. Removed the front wheel then removed the fender innerliner.

It has been a year since I did this, so the 'instructions' may be a bit hazy!

Since I was not disconnecting the battery (new to Audi A8's, and understand this may result in some issues with electrical systems, so did not do it), I put on a pair of latex gloves and a pair of goatskin leather gloves to do the job.

From there on, it is just removing (twisting off as I recall) the ignitor, disconnecting the bulb and removing it. Carefully install the new bulb with correct orientation, make connections and install the ignitor.

Check to see that everything works (ignitor could be the problem, not the bulb), before installing the fender liner and the wheel.

Gary-

 

Not sure if all the terminology in the title is correct. I searched for instructions for a long time on how to change the driver side bulb. After paying the dealer ~$350 to change passenger side about a year earlier, figured I could DIY this.
Given you're reading this, you're handy enough to get it done. My first attempt (garage, back to PC, garage, new PC search, etc.) took about 4 hours! If I have to do it again, maybe an hour start to finish.

I couldn't get at the bulb by removing the power steering reservoir alone. Finally gave up on this and jacked the car up, removed wheel and then removed liner.
Liner was a PITA, given dirt sand, etc. Removed the Torx screws (3 or 4?). There are 2 types of grommet-style clips. One takes a 1/4-turn with a quarter (coin). The other needs the center pin (black) pushed all the way in. Yes, IN. If you're having to pull hard, you're doing it wrong...I broke a couple of mine.
Then you manhandle the liner out.

Can now see back of bulb housing. Back cover held in place with 2 clips on top. Press down on tabs and cover tilts back. Take this out.

Remove clip from behind ignitor and remove ignitor (silver box). Remove 2 clips from bulb and take out bulb. Replace in reverse order.

I had one additional problem (frustrating hour) in that the ignitor would not reinstall, ie couldn't turn it those few degrees back into position.
Simply, there's a nylon (tan colored) ring below the outer (black?) ring. make sure that the two spaces align. I used a toothpick to move the nylon ring. Ignitor went right back on.

Hope this helps someone!