How do i get rid of my belly fat? help please ha..?

Well i am 15 years old, i weigh 107, im 5'2. I have belly fat that i really would like to get rid of so i can look better. I am 3rd in the state in cross country AA, and 6th in the state for track, i play a lot of basketball too, i am very athletic. Im always doing something, and i drink a lott of water, mostly all i drink besides occasional gatorade and ice tea. i do eat junk food dont get me wrong, and i also eat late at night due to sporting events running late. I just dont understand for how athletic i am why i have belly fat....if you could help that would be great! Thank you