HELP ME LOOSE WEIGHT!!!!!?

I'm a 10 year old girl and going into 5th grade.There is a Beauty pageant coming up and I'm a little overweight and would like to know how to loose 20-30 pounds before September.. I weigh 100 pounds and I'm 58 inches tall...PLEASE HELP!! p.s.10 points goes to the one with the best and detailed answer!!!!!!!!!!