You can't lose weight that fast, especially in a targetted area such as the stomach area. You could lose a few pounds in a week, by decreasing your calorie intake, eat plenty fresh fruit and veg and drink plenty of water, don't eat any unhealthy meals or snacks, no fast foods or unhealthy drinks, fizzy drinks ect. Fresh Juice is fine.
A moderate amount of exercise will do you a great amount of help, but don't over do it, if you blitz of exercise and hardly eat anything then your not helping your self and you won't lose weight, or if you do then you will put it straight back on again afterwards, plus it's unhealthy.
Like i said, moderate exercise, light jogging, maybe some swimming< great exercise and easy on the joints, walking, burning fat exercises are the best, cycling is good aswell.
Slowly is always best, and i can guarantee that if you can lose a few pounds in 1 week by doing this, and it's the healthy way, a few pounds does make a difference to the stomach area deffo, imagine dropping a few bags of sugar. it's a lot.
Hope this helped.