The number of calories you need each day depends on your activity levels and your body size. Your diet is the key factor that affects your weight and health.
How many calories should i eat
The first thing you need to do for lose weight is determinate the calories that you need a day.
The second is begin cut down the extra calories means change your diet and make exercises for burn these extra calories.
You need cut down 500 calories a day to lose 1 pound a week or 1,000 calories a day to lose 2 pounds a week (1 and 2 pounds a week is considered safe rate to lose weight).
Hope this help