How much weight do i need to lose??

heres the deal....i am 15 years old , about 4'11 or 5'0 im a little flatchested , i love to eat junkfood , i weigh about 140 pounds and theres this girl in my cl i think she is sooo pretty and shes so tiny shes a senior and she drives and the guys jus cling to her im a big fatty and shes tiny so........ heres the deal........ i wanna be able to wear skin -tight- tight clothes and not have fat showing how can i do that and how long will it take pleaze help me thank you for your time