How can i get over my fear of heights and roller coasters?

okay well in 2 weeks my grade is going on this trip to hershey park. i went last year, and went on my first roller coaster last year. it was super fun, but it wasn't that bad. im just scared of the ones that go upside down, and im really scared of heights. and my group is full of people who love upside down roller coasters and stuff, and they want to go on farenheit, which i think has the 2 biggest drop in the world? so how can i get over my fear of heights/roller coasters?