Decrease carbs. Abdominal fat is the most dangerous fat increasing your risk of heart disease. It responds best to decreasing your carbohydrate intake (breads/pasta/cereal/pastries, alcohol/soda/juice). You still need lower total calories (500/day to lose 1 pound/week), drink alot of water since obesity is dehydrating, continue with exercise.
Healthy changes. It's not realistic to target weight loss in one particular part of the body. It is more common to lose weight overall just by exercising and diet. The key is to consume less calories than you expend. You can do sit ups and abdominal exercises but you won't see anything until you lose weight overall. Try replacing processed food with natural to start off. Good luck.
Weight Loss. Aside from what my colleagues have already mentioned, you might want to have your thyroid and growth hormone levels checked. It is a known fact that as you age, growth hormone levels decrease. A low level causes a decreased muscle mass and an increase in abdominal girth, or a redistribution of weight or fat. Avoid anything that has high fructose corn syrup or hfcs.