Exercises- walking briskly, jogging
a small amount of running
, too much running
can be bad for you and your bones as your still young and developing. Horse-riding, swimming, karate. even like using a skipping rope or trampolining half an hour a day can make a difference.
I would also recommend cutting out or reducing sugary and yummy foods, this will include fizzy drinks, sweets, chocolate, cake, biscuits, crisps.