As the other posts will mention, GRE scores vary according to schools. Some universities may average your scores, some may take the highest score, and others compare your "first" score with your other scores to see whether your scores have improved.
The company that runs the GRE (I think its called ETS) reports all scores in their score report. Its up to your school to decide which one they want to consider. After a certain number of years however, your old scores will expire.