How can I lose 15 pounds?

I'm 15 years old and I want to lose 15 pounds or more within a month and a half (before school starts). I want to start keeping track of how many calories I consume. I want to consume at least 1200-1300 calories a day. What I need help with getting motivated to exercise and staying away from junk food. I also don't know what exercises I can do to lose the weight and my love handles.... And how many calories should I burn a day to lose 2 pounds a week? What should I do?