There are two small screws with pointed ends whichhold the headlight retaining ring and headlight to the headlight "bucket". Those are not adjustment screws and are for removal and replacement of the headlights only.

The other two larger screws are adjustment screws which are in notches in the headlight bucket. One is located on the side of the headlightforhorizontal(side to side) adjustment and one is above the headlightfor verticle (up and down) adjustment. Do not remove those screw because they arefor adjustment of the headlights only.

GM has used that designto adjust orreplaceheadlights as far back as I can remember and believe me, that is a long time.