I was almost like you in primary school. If you don't exercise, you can't lose weight. First of all, you should put an end to all snacks and fried foods and all kinds of junk food. You are still young, it is impossible not to eat dinner. You must run every day, but don't run too much. You can start at 400m and then increase it. Let your body adapt. You will find that weight loss exercise is boring and difficult to do. Believe me, regular exercise is the best. I realized it in high school. I lost 60 pounds a year. I hope it helps you.