Read your manual, it's in there.

Quick answer for you though.
There is a place on the housing itself (pop your hood) on the side, and one on the back, that adjusts the left/right as well as the verticle alignment of the headlight itself.

You'll see a level and that tells you the verticle alignment, to judge the horizontal alignment you'll also look at that level, but it will turn left or right.

The manual has more detailed instructions as well as how to properly adjust the height (what height to put it at).