How does a thick 14 year old girl loose weight?

im almost 14. but my friend says im thick. lol i have bigger theighs but they arent huge. i have a big butt too. im like 5'3 yet i have a belly /: i want to loose that belly i dont mind the butt thing though! haha jk but i wouldnt mind if my theighs were a little smaller.. but i want to loose my belly well most of it before school starts.. any help ? please dont put rude answers either. thanks!