Stop drinking soda all together, it'll help you in the long run.
Soda is not good for much of anything. It is dehydrating, carbonated, full of sugar and sometimes contains artificial sweeteners. All culprits of an uncomfortable bulging belly. Think about it, each time you sip a carbonated beverage you are swallowing little gas bubbles that go into your stomach. Those little bubbles all add up into one big gas bubble that you feel and sometime even see. Belching can sometimes relieve this pressure partially, but dropping the carbonation all together is the best bet.