16 years old, 250lbs, 5'10 - Best diet plan?

Hey all, I'm 16 years old, 5'10 and weight 250lbs, i hate the way i look (body wise). Recently i've been doing 30 - 40 minutes exorcise on a treadmill for 5 - 6 days a week and about 2 - 3 late walks at night with the dogs (30 minutes a night). Few months back i weighted about 265lbs, which I've Lost 15lbs within those months (about 2- 3 months). Though, I've hardly changed my diet (cut out sweets, fizzy drinks). So what would be the best diet plan for me, and what would be an achievable target?