I need to loose weight, drastically

I'm 6ft 1in and 300 lbs and I'm 18 years old. I haven't really cared about my weight, but i guess it'll become a health risk later in my life, so i need to do some thing about it. I need some advice on what to eat, and an exercise routine, I've always been very athletic, but i don't think i can start running right away, I've been told thats the best way to loose weight, to simply run. I'd be ok with that if i wasn't 300 lbs. So I basically need a starters guide on how to loose allot of weight fast. so i can beggin a more work out regiment.