It is not possible to lose fat from any particular area in a week.Fat loss is a slow process and if you want to reduce belly fat you should first of all fried,junked,processed,canned foods and also refined cereals.It is very necessary to combine a healthy diet along with exercise.So,take whole grain cereals,include lots of fresh fruits and vegetables,proteins and healthy or unsaturated fats and also drink plenty of water.Exercises are also important as much as diet is so take out 40-45 minutes for your exercise like you can go for walking,jogging,running,swimming which will help you to lose overall body fat as well and particullarly for tummy you can do crunches,reverse crunches,, Alternate heel touch,Oblique abb crunches,etc under guidence.will help to tone the abdominal muscles and will help in reducing tummy.