fat kid trying to lost weight

http://iifym.com/tdee-calculator/ Use TDEE calculator to calculate your approximate maintenance calorie intake. You need to create calorie deficit like minus 500 cal from your maintenance level. You will find you lose 1 lb weekly gradually.

If you want to preserve some muscle, eat enough protein (0.8 per pound of your body weight). Try to get a kitchen scale to give you idea of how many calorie you are eating daily. You need to make adjustment to your diet.