Headlights are adjusted with adjusting screws. Some cars, typically Hondas and Acuras, have an adjusting bubble level that aids in adjusting the vertical aim but not the horizontal aim.
A Phillips head screwdriver or torx wrench, masking tape, measuring tape and possibly replacement bulbs are needed to adjust headlights. A length of flat, level ground at least 35 feet long and a flat, vertical surface like a garage door or the back wall of the garage are also needed.
Aiming the headlights is best done after the sun sets so that the path of the beams can be clearly seen. If using the back wall of a garage, this can be done with all the lights turned off.
Begin by parking near the vertical wall, and mark the horizontal and vertical centerlines of the entire headlight enclosure on the wall using masking tape. With the masking tape, mark another set of lines both below and to the right of the original lines. This second crossing of masking tape is the guide used to aim the headlights. This offset is done in consideration for oncoming drivers so that the headlights are not aimed directly at them.
Use the measuring tape to move the vehicle back from this wall 25 feet. Some vehicles' manuals indicate a different distance. Bounce the car at all four corners to ensure that the suspension is properly settled.
Turn on the headlights, and use the headlights' adjusting screws to match the second set of masking tape marks made earlier. Check the owner's manual to find the location of these adjusting screws, but they are usually located on, or near, the headlight itself. On some cars, these may be behind the headlight assembly or otherwise out of sight. Make adjustments one quarter of a turn at a time, then check to see how well the headlights are aimed. Repeat this process until the headlights are aimed to their proper locations.