Are you shooting with open sights or scoped? Since the sights are on the barrel if you're shooting open sights this should never be a problem unless the barrel is defective or the velocity is REALLY low. There are a number of cures if it's scoped including bending the barrel and droop compensating mounts to fix the symptom or finding and fixing the actual cause of the problem. More information would be good.
Lowering the rear sight will further lower the POI. The front sight must be lowered or the rear sight raised to raise the POI.