You are not advised to do dieting in this age. Because it is growing age. You need food & energy to grow & get certain height.
What you do join some game which you like.
Play regularly .at home or school where it is possible .
Take part in house old work so that you can burn your energy.
Only have a check on chocolate , sweet meal & junk food. Always take milk . It is very important for your height.
If game is not possible, run fast daily for 30 to 40 mint .