1) You will need to burn off excess fat around your abdominal areas
2) Need to get your abdominals strong
The time that this will take, entirely depends on your present body composition, your food habits, whether you are sedentary or active, how stressed out you are usually, your genetics….
Nutrition/Food habits, are perhaps the most important factor, which is under your control. The basic thing to understand regarding Nutrition is that, in order to reduce excess body fat, Calories In need to be less than Calories Out. On top of this, the average person needs to ensure that they are eating less Carbohydrates and more Protein and Healthy Fats, as part of their diet.
Switching to a more active lifestyle and adding in some workouts to get stronger, will definitely speed up the process.