Get a better diet. Eat more whole clean foods like chicken, beef, pork and fish. Cooked meals. Include vegetables. Yummy! Avoid fatty, oily, crappy foods and chips and candies. Waste. I'd rather eat delicious home cooked meals or a sandwich with roast beef than muncing on fried stuff. Got it? Eat better. In line with this, try to eat less than what you are eating now.
Exercise. Look for a sport that you would like and enjoy: Soccer, swimming, basketball, badminton, or martial arts.. and stick to it! At a young age, you should find a sport that you can excel at, and stick to it. Not just for personal achievement but for health purposes. Have fun with it while burning that fat off!
In summary:
Diet - Clean up your diet. Eat cooked meats and vegetables. Lay off the chips and candies. Eat eggs, milk, yoghurt, fruits.. Lots of delicious healthy stuff out there. Moderate your eating. Eat less if you wanna really lose weight.
Exercise - Go for a sport or activity you enjoy doing and stick with it. Try also walking for 30 minutes every day.
What'll happen?
You'll improve your health, lose weight, be healthier, be a stronger individual and go to your healthy weight for the LONG TERM. There are not HEALTHY FAST WAYS to lose weight.
You wanna lose weight very fast? STARVE YOURSELF. Or do 10 hours of running and cardio. Sounds like something you like? Of course not.
Stick to moderate eating and exercise. Give yourself patience and time and you'll get better. :)