What is a good weight for a 13 year-old? and How can i lose some?

heyy :) I am a 13 year-old i am a little tall for my age, i have really muscle legs, i also have brood shoulder's i have jelly belly witch i don't wont any more. I weigh about 105ks to about 110 what can i do to get it all of i wont to be abile to wear pretty clothes i the summer!!! =D What is a good weight for a 13 year-old? (With diet i still have to go to school)