How to lose weight?

So I am 16 and I weigh 200lbs. I am totally overweight and no matter how hard I try to eat healthy I always fail. I get tempted and I really can’t deal with it. I need help with saying no to those foods and also I go to a gym what should I do to burn a lot of fat? I start school in a month and I want to lose some weight by than. Also my formal is in December and I want to look good by then.