How do I get over my fear of heights?

When I was little I thought nothing would be cooler than to get on the kiddie Farris wheel. I got on and as soon as it took me up I instantly got scared because I realized how high up I was! I want to go on Roller coasters but Im too scared to, I don't like going up really high and just being dropped down, I just don't like that feeling. However this summer I want to change that because a few friends and myself are planning on going to Universal Studios. I don't wanna be the "chicken" in the group and not get on any rides. So how can I get over this fear of heights?