On 2003's (and probably 2004's) there are 2 black plastic OEM brackets that connect to the headlights.

Each bracket has 2 bolts and 2 phillips screws.

I adjusted my headlights by loosening only the two bolts, which then allowed me to tilt the entire headlight (and bracket) up or down ~~1 degree, then you tighten those two bolts back (the bolts will tighten in a slightly different position based on how much you moved the bracket+headlight to adjust your beam).

Easy. Don't mess with the 2 phillips screws when your sole purpose is adjusting headlamp angle. Those 2 phillips screws are for connecting a headlight to the black plastic bracket.

The 2 bolts connect that bracket to your Disco...and sliding that bracket slightly forward or backward on your Disco before tightening those 2 bolts will adjust your headlight beam up or down as desired.

Push the bracket toward your driver seat and that tilts your beam up a bit.
Pull the bracket away from your driver seat and that tilts the beam down some.