What easy things can I do to slim down?

I'm 16, 5'4 and weigh 162 pounds. I need some easy ways to slim down. I don't want to go on a full out diet but I need to lose some weight. I don't drink sugared soda, I only drink diet and I drink plenty of water, but I also have foods like doughnuts, pizza and stuff like that. I don't want to exercise constantly, what are small things I can do that'll add up to help?