How do I lose weight when I'm only 13?

You don't.

Unless you are extreamly over weight. In which case, talk to your parents, and have them take you to and talk to your doctor.

Good luck hon

Simple hun... Food moderation and exercise.

But there are literally thousands of diets and exercise plans, the trick is finding one that works for you.

I eat six smaller meals a day and incorporate 30-60 minutes of cardio and weight-training 5 days a week. And it keeps me at a healthy size.

Can you give more details on your weight, height, lifestyle, what you eat, and how much?