Cycling alone isn't going to get rid of belly fat. You also need to do some full body intense resistance training and clean up your diet. Eat foods which are very high in fibre. Try to fuel your body with complex carbs instead of refined carbs... If you're eating a lot of carbs, then lower your fat intake. If you're eating a lot of fat, then lower your carb intake. Keep your protein intake a little higher. Experiment and see how your body responds to different types of food, and at your young age I would definitely try to build some muscle.