Myth: If you have a tummy, if you do enough sit-ups, it'll go away.
Fact: If you do enough sit-ups, you'll have rock-hard abs underneath that tummy.
There still seems to be this persistent myth that muscle can "turn" to fat, and vice versa. That's biological nonsense. That's like saying your hair could, somehow, turn into fingers. It's made up of different biological "stuff."
The only things you can do with fat is burn it or add to it. Period.
And, unfortunately, your body does not select which fat to burn based on what part of your body you're working out. It will still pull fat from the next place it has set up to pull fat from.
On the other hand, that might be fortunate. Because what it means is, you don't have to work your abs harder than any other part of the body. Do a few exercises for it, just like you would for your chest or your back, to make it stronger. Follow your normal combination of a healthy diet, cardio, and weights. That'll get that belly down, and insure there's something nice under there when it's gone.