What is the fastest way i can lose weight (40 to 50 lbs) in a 4-6 month time frame?

Depends: It depends on your starting weight along with current body fat percentage. You may realize you don't need to lose that much..... But a very quick way is to go on a 1000-1200 calorie diet. Some weight loss docs will go lower but make sure there is weekly supervision. Make sure you keep your protein high though (about 1 gram per pound per day).