This all depends on you! Protein powder alone won't lead to weight loss. However, with a balanced diet and exercise program, protein powder can be a great addition to any weight loss strategy.
It is generally recommended that you lose no more than 1-2 pounds per week. To achieve this, try cutting 500-1000 calories from the amount of calories you normally consume per day. To estimate how many weeks it will take you to achieve your weight loss goal, divide the total number of pounds you'd like to lose by the rate at which you are losing them (1 or 2 pounds per week). Of course, if you are already eating relatively few calories, you should avoid cutting too many calories from your diet.