How do i loose weight fast!?

im 15 years old, im 5'3 and i weigh about 135 pounds! i really need to loose weight before summer! i try everything i can, i do situps everyday, i walk, i dance, but the problem is i keep drinking soda and eating junk food. help me get rid of that stuff and stop me from eating so much! also, what are some other exorcises i can do? i cant run outside because there is snow everywhere :/ plz help!