Whats the best way for an overweight person to prepare for the military?

Im currently planning on joining a branch of the military, unfortunately I'm very overweight. I'm 6'3" and I weigh in at just about 315lbs. Through my life ive been a slacker as well as a computer nerd, I've played football on and off for a few years because of my good body type for that kind of thing so im not new to exercise. Unfortunately it has been about 2 years since ive played and i havent gotten much exercise to be honest. Im wondering if anyone knows a good exercise plan to help me get back onto my feet when it comes to this. I have about 6 months until i plan on enlisting and the branch im most interested in happens to be the Air force so hopefully i can use this time to reach their weight limit (220 lbs max) Also if anyone has suggestions beyond the air force just let me hear some things =) any help is definitely appreciated