Incorporate strength training. While it's true you'll need to lose the fat over your abdominals so that your muscle tone can show through, don't rely on cardio alone to get the job done. Muscle will help reshape your body and allow you to actually burn calories while your body is at rest, not just when you're hitting the gym. Studies show that those who lift weights have a lower fat mass percentage than those who do aerobic exercise alone.
During your teenage years your body is changing and growing in all sorts of important ways. Losing weight is possible but you will want to be careful to do so safely so you don't end up causing health problems. Talk to your doctor about your desire to lose weight so they can make sure there isn't an illness causing you to gain weight in the first place, and so they can help you identify ways to lose weight safely while still having a healthy body.
For a flat belly, put down the chips and cookies and snack on some air-popped popcorn instead. The air-popped stuff doesn’t have the salt and fat that comes with unhealthy microwave popcorn that’s usually doused in butter, and it’s also an excellent source satiating fiber and protein. In fact, one cup of popcorn popped fresh in olive oil and lightly salted has 2 g of fiber, one g of protein, and is only 40 calories. To add some flavor to the tasty, low-calorie treat, make use of metabolism-boosting spices such as cinnamon or cayenne pepper. For more ways to boost your fiber intake, check out The 43 Best Foods for Fiber!