That would be my suggestion too. You're obviously motivated, so go join a gym and talk to the staff there. That's why they're there - they'll be only too pleased to tell you what you need to do.
But in general terms: cut the burgers and KFC you eat, grill rather than fry, have boiled spuds rather than chips, and eat more salad - especially when you're after a snack. Take up cycling or running, use the stairs rather than the escalator or lift, and most importantly find someone to go to the gym with - you'll egg each other on.
Also be aware you won't see noticeable results in the mirror for a few months, and results are gradual even then - but when you meet someone you've not seen in a while, and they comment on how you've toned right up, it's worth it... ;-)
Good luck mate!