You should have a bolt (8mm or so) on the back-top of the headlight buckets. It looks like it has a washer with sawtooth teeth under it. Turn those (can't remember which way) to adjust the headlight up or down. I can try to get a pic if you can't find them, but they're the only bolt on the back of the bucket.
2004 Frontier, King Cab, XE, 4x1, 4-cyl, 5-spd