I am 17 years old, how do I loose weight from my stomach?

I am a junior in high school and I am very athletic, however that doesn't seem to stop me from gaining weight. It's not that I have bad dietary habits. I have recently stopped drinking soda, and all I drink is water now. What else should I cut out from my diet, and what should I start eating in order to loose weight? I run track, and although the season has not started I condition 2 times a week. Also I play tennis recreationally outside of school twice a week, and have speed camp after school 3 times a week. I lift weight regularly. What else can I do to get rid of my stomach? And what are some good ab exorcises?