I weigh 170 and 5'1 , iam 20 how can ii lose weight fast?

Weight Loss: Weight loss should always be a gradual process -- aim for 1-2 lbs. Per week through diet and exercise -- this is sustainable. Rapid weight loss usually does not work, and leads to a weight "yo-yo" with rapid gains and losses.

Diet and Exercise: Several things to consider. Look carefully and honestly at your diet. Cut out all unnecessary calories such as sweets, high calorie snacks, sodas (unless diet), and fats. Consider a vegetarian diet for a month or so. Begin an exercise program of some sort, at least walking. Hopefully you can lose 2-3 pounds a week. It is all a math problem. Calories in versus calories burned up! good luck!

Food volume : Don't eat so much. Eat 4 times a day, no more than would fit in your hands cupped together. Of course, choose reasonable types of foods. Then, if you're so incline, increasing activity wouldn't hurt.