Firstly, calculate your BMI and if your BMI comes in the range of 20 to 25, then you don't need to lose weight. Only if it's more than 25 you need to lose weight.
Here are a few tips to reduce weight.
1. Drink lots of water.
2. High protein, low carbohydrate diet must be followed.
3. Intake of calories should be less than the daily requirement, and you should get most of the calories from fruits and vegetables.
4. Avoid rice and rice products. Green tea twice a day.
5. Burn more calories than you have taken. Cardio workout must be followed. Any form of excercise which keeps your heart rate raised to a level of 140-150 burns fat effectively.
6. If you are very dedicated and follow all these sincerely you would be able to lose 15kgs in 4 months.
All the best.