Dangerously, and in ways that will guarantee gaining all of it back...and possibly more. The only way to lose weight for good is to do it the old fashioned way.
You don't. I don't know how much you have to lose, but most likely, you didn't gain it, overnight, and you won't be able to lose it that quickly, either.
Safe weight loss is considered to be 1-2 lbs/week, accomplished via healthy diet and moderate exercise.