Very generically, you need to be on a caloric deficit. 500 cal a day deficit will allow you to drop the weight safely and your skin should be able to compensate and stay tight. Lose it too fast and you will need to get the excess skin cut off. Doing cardio is a great way to burn calories, doing several sessions a week at 135ish bpm will really help burn fat. Do it for at least 20 mins, but longer does burn more calories.