Eat healthy and often. Small portions and if you can't understand the ingredients, it's probably shit. Veggies, fruits, lean meats, etc. If it's sweet and comes in a plastic bag, it's not for you.
Exercise. Crossfit, P90X, etc....it's all just bullshit you can do at home for free rather than spending thousands a year for someone to tell you that increasing your heart rate will burn fat. Running is also cheap. Pull ups, push ups, leg raises, crunches....all easy to do at home.
Get older. If you establish a life around taking care of yourself at the age of 14, by the time you're my age you'll probably be very happy with yourself. You get better every year as you learn more and grow.