How much green tea should i drink to lose weight??

im really desperate to lose weight, im hypothyroidism so its really hard for me to lose any weight at all except when im really sick...i drink green tea at least once a day and i drink a korean green tea that is 0 calories...i heard that green tea can help you lose weight..how many cups of tea should i drink each day to lose around 20 pounds but in a healthy way so my body doesnt lose just water weight...i really need this weight loss to have long term effects