How to loose belly and chin fat?

I am not rily fat just overweight plus i have a lot of muscle but i still don't raly like my appearence, i hav a little pudge under my chin and some belly fat but everything else is fine, i'm 5'6"and weigh about 150 so i could loosed 20 lbs maybe 30 but cuz of muscle and my body buil more like 15 20 i want to loose at least 20 lbs by august 3 so ill look good for school i wear a size 11 in juniors pants and a medium in shirts but i still want to be slim and pretty plz help!