The old school method of lots of exercise. Your may want to change you eating habits too. Go see your doctor and dietitian to get you started with the nutritional aspect.
is there any method to reduce my waist size ?
Eat breakfast. It might seem counterproductive to eat if you're trying to lose weight, but studies show that eating breakfast within an hour of waking up keeps your insulin levels steadier and your LDL cholesterol levels lower.[1]Building a healthy breakfast:
Choose a protein: Eggs, beans, peanut butter, nuts, lean meat
Choose a fiber: Oats, fresh fruit, leafy green vegetables
Minimize refined sugar: Avoid sugary cereal, pancakes, pastries, instant oatmeal
Tip: Oats and other low-GI carbs maintain healthy blood sugar levels, making it easier to lose weight
Less sugar and do workouts and exercises focusing on your tummy.
There are special exercises just to firm up the abdomen which will reduce your waist size. Look for some Pilates or yoga DVDs.