DISCLAIMER: I am DEFINITELY not a healthcare professional, consider this when reading, thank you.
Adjust your diet, not drastically- you don't want to get obsessed or end up in a bad way- but do consider what you eat, and how much you eat.
I'm lazy too, and on my first day of a "gradual cutting out the bad stuff" thing. If you find that the bad things are in your meals, maybe voice your concerns to your parent or carer, and maybe request 'healthier' options, if possible (healthy doesn't always have to be boring, even though it sounds it...!). Or if they're not, cut down on any snacks you may eat (for example, I'm especially bad with crisps, ice cream, and chocolate, so chocolate was the first thing to go, next week, crisps, and then I'll just have to see how it goes), even try substitution, fruit, vegetables etc.
Research healthier foods, get yourself excited about eating healthily but DO NOT get obsessed, DO NOT take diet pills at your age (not being patronising, it's genuinely not good for you before full bodily development) and please NEVER make yourself throw your food up or anything. It's detrimental to your health. Apologies if you think I was OTT with the last one, but, seriously, do not ever.