Make your own plan according to your physique. Although the weight of thirteen years old is a little heavy, it is only a long body. It is recommended not to go on a diet to lose weight. It is recommended to eat more fruits. Drink more water, water is a good medicine to lose weight. Drink a glass of water every morning and a glass of water before three meals a day to control your appetite. Don't drink more water before going to bed, especially after ten o'clock. Another key is more exercise.