There is a "how to" here that has you taking off the fender liners, don't do it this way, it's lots more work.
Using a 10" Phillips screwdriver from the top is how the factory manual says to do it. Follow this metal strip down toward the side of the HID beam and you will see a hole, look in the hole for the little gear teeth, put your screwdriver in there and turn.
Clockwise - Up
Counterclockwise - Down
What I do is go to a parking garage and put the car 8' from the wall
In this pic I had it set at 26" from the ground but have since moved it up to 27", that seems to be the "just high enough" not to bug people to bad. Nobody has flashed me yet and it seems to cut off right at the top of the average trunk.
Notice the hot-spot at 26" that is what you are measuring to.
Good luck
Chris
I keep meaning to take a picture with the screwdriver in the hole so you can tell where it goes, I'll see what I can do about that today.