Weight loss help :) ?

I am a girl, fourteen years old and 5' 5". I weigh 122. I really want to lose weight, mainly from my theighs, , and abs. I want to lose 10-20 lbs. My exercise regimen basically consists of softball on Monday, PE on Tuesday, and PE and softball on thursdays. Anyway I was wondering abou how many calories I should be eating daily in order to lose about 1 1/2 pounds a week, and also what other exercise should I be adding? Also any dietary and/or exercise tips are appreciated.