There are two ways to reduce and combat prejudice and racism on a large scale.
First is education. If it is taught that being racist or holding prejudice against someone un-necessarily is wrong, then it will eventually stop. However, the way in which it is taught is very important; rote learning, or taking notes from a textbook about it will not help very much.
Second is reducing social attitudes towars accepting prejudice and racist behaviour. This ties in with education, but awareness of what the consequences are of being a person who holds prejudice or is racist to another person, may help prevent recurring negative behaviour. If it were seen in society as a negative thing to be a racist or a prejudice holder in all groups, then the problem would easily be eradicated.