How do I lose my belly?

So I'm 15 years old and in January I weighed 186 pounds, now I weight 157, and I've definitely noticed it. I've shrunk 3 pants sizes and i feel a lot better. the problem is in my belly. I can't seem to get rid of it ! I try doing workouts that target those areas, but I can't stick to them, so to lose weight I use an ellyptical. The problem is mostly my lower belly ( HATE it) and my obliques (stick out..) Why haven't I lost these yet, and will they go away if i just stick to regular cardio? thanks :)