Workout Plan/Dieting for summer?

I am a 16 year old female and want to really tone up my body. So from now until school starts (Sept 4th) I would like to lose at least 15 pounds. How can I do this? What workout plan should I go by? What should I eat, how many times a day, exc? And lastly, how to not eat junkfood..that seems to be my hardest problem.