What is the quickest way to lose weight for a 13-year-old gal?

I am 13 yrs old, 5 ft 2 inches and weigh 107 pounds. I'm really upset with my body and want to get thin before school starts again, it's always been a problem and I want to take action... I don't know that much about what I shouldn't eat (like normal stuff, I was surprised that pasta was really bad..) so please list those if you can! I just want a way to get thin without it backfiring & anything is fine, write your method of keeping in shape. Also..I was curious if cereal is super bad for you. Like Raison Bran and stuff. Thanks!