How do i get my fat on my hips to go away and my belly fat to go away in a short time for a swimming party.hel?

I'm 13 and i weigh 120. ya yikes! im skinny, but i have some belly fat and some fat on my hips like there somewhat big. and i am tired of not being able to wear clothes that shoe my hips.! its so embarring! and i need to fit into my dresses for church. Please HELP?!?!!? also i have a swimming party an a lil bit! and i want to look good. Please Help?!?!?!