Cut out sweets, bad fat, and dairy. I would reccomend going to the gym but if not then get some free weights and a bench. Lifting weights will not burn much fat so try to go running, biking, or something cardiovascular atleast 3 or 4 days a week for about 20-30 min. Do as much as you can, push yourself, make the cardiovascular harder when you get in better shape. How old are you? still in school?
Ben