Exercise is the most effective way to combat caffeine addiction that I know of. Endorphins that you get from doing brisk exercise for at least twenty minutes a day give you a similar, more natural effect that have a lot more benefits. Look up some of the benefits of cardiovascular exercise and the effects of caffeine to get yourself educated so you're conscious of everything your body is doing. If you plan on losing weight through exercise, it's a good idea to give yourself variety: Cardio, muscle endurance, and muscle strength all need to be worked on in effective weight loss. A good diet will go a long way, too.
I don't recommend cold turkey with caffeine, unless you've got a will of iron and don't mind a few headaches. Your body's used to something, and depriving it very suddenly can throw you off balance - Caffeine stays in our systems for a surprisingly long time, depending on our metabolism, so a dependency on the stuff may be longer reaching than you think. It sounds like you've had a taste of this, though, and if a small headache and some tiredness is your only problem, you'll probably do just fine cold turkey. If you do decide to moderate until you stop entirely, there's plenty of plans and self-help guides out there that can give you a good direction and an idea of what to expect.
The biggest part is to just stick with your decision. Remember that you are in control, and that you're the boss of your own body - And don't beat yourself up over having an occasional soda. You'll know the difference between addiction and recreation when you drink for taste rather than the desire to increase your energy. Even if you're doing an all-nighter, try to resist. One excuse is all it takes to fall back on old habits.
Good luck!