I know this is an old thread, but since I stumbled on it looking for an answer myself to a related question (my dipped xenon/HID/gas discharge headlights beam was way too short, not reaching past 7m on the drivers side — the distance was never the same on both sides), I visited a dealer to adjust this (among a few other things I had them do).
However, they done nothing and since it's more expensive for me to spend time driving to them and losing another couple of hours, I managed to find how you adjust the height of the beam on OEM Alfa 159 xenons yourself.
If you open the hood, you can see two bolts protruding from the headlight. The outer one is to adjust the height, and the inner one to adjust the direction (supposedly: I haven't tried that one). I got it to raise the beam by "unscrewing" (for regular direction screws) the outer bolt.
Photo of the back of right side headlamp
itself with green arrow pointing to the height adjustment bolt and red for the direction adjustment: as you can see, you'll need pliers or the appropriate wrench.
Note: you can get to this without taking the headlamp out. I simply had this photo handy.
I've used this to get my headlights back to at least 20m for the drivers side, though now looking at how much of the road they need to light up (40-80m in Serbia for the short beam), I'll be adjusting them further.