You cannot lose fat in a certain place. There is no way to spot fat reduction, unless with surgery which is not an option. The weight loss will come with overall fat reduction. Doing crunches, sit ups, etc will only increase your waist circumference.
It is not as simple as concentrating on your abs. I recommend doing lots of cardio, building muscle causes hypertorphy, which will actually increase the circumference of your stomach, so you will actually be increasing it, but still keeping fat over it. Lose the fat, then build the muscle to tone.