First of all, you have to go on a diet and eat 80% full at every meal. No snacks. If you are really hungry, eat less fruit.

You are still in high school, so you may not have much time to exercise. You can skip rope for 20 minutes every day. When skipping rope, try to master the rhythm. Relax your calves as much as possible. It is good for the overall body shaping. Then you can pull down the ligament or something.