How do I stay in shape?

This past year I gained 49 lbs. I really thought I was doing ok until i looked in the mirror and my shirt was ripped. I really started to flip when all my belts ripped when I put them on. What should I do to lose the lbs? I'm on the track team, and I'm scared my career is in jeopardy. Should I eat ice cream or something? What could I do? My dad said videogames may help a bit, but my dad dropped out of West Virginia, so I don't know if he's a good source. Please help or I will never be able to run again!