Start with losing the weight by creating a healthy diet and doing a lot of cardio. Then you can work on gaining muscele. Do weights at your local gym and do a lot of push ups and pull ups (you must be able to at least do 12 of these to become a soldier, at least my dad did and he was in the navy it's probably similar.) hope this helped
Work on your push ups and sit up. You can google army fitness charts and find out your standards for you age group there. You will have a low min to join but will have to do 45 push ups and 50 situps to graduate basic training. Most people have a hard time with their run times so practice your two mile run and try to do it in 13 min. You should be all set by then!
The army will help you lose the Lil bit of body fat. They didn't use to do pull ups just push ups. Sit ups. And 2 mile run. But going through basic will help with all that and build muscle. You just have to pass a physical and have a high enough ASVAB score to join. The work out stuff is started in basic