Best and good way to slim down is to exercise. But be mindful of your weight and body condition. If you are above 35, and have not been exercising for a long time, better to seek doctor advice before doing so.
Upon doctor approval that you are fit to exercise, if you are overweight, do not do jogging or running. Bad for knee. Do swimming or cycling or other non impact to knee exercise.
Min duration of exercise is about 30 mins at Heart rate on average around 130 beat per min. That is the fat burning zone. Do it like 3 times a week and you will see result in 3 months.
Maintain your food intake.... take smaller portion in between meal so you wun go hungry all the time.
Good luck and wish you all the best,