How can i lose weight?

i am 16 years old and weigh 155, 5'6, and size 6 pants. i dont feel like im where i want to be with my appearance. i want to lose 20-30 pounds. but its so hard. all we have everyday at my house is junkfood. and i stopped excersing since track was over. so i need to know a good routine to get going on so i can look good in a bathing suit for summer :):) please help!