Weightloss tips to lose weight?

SInce I was young always been active I've done soccer, boxing, karate, volleyball and basketball...I've always been on the heavy side.( i'm 16 and i am 210 pounds) I dont know why..I get plenty of excersise a day and I eat healthy! The weight just never comes off! It's like I gain more than I lose...This summer I really want to lose weight and come back my junior year of high school smaller and healthier...so any good tips? please I am very desperate at this point.....