I want to incress height?

Wear high heels ...: At 21yo, your growth plates might have fused. If an xray shows your bones have stopped growing due to fused growth plates, there's no easy way to grow taller (ilizarov procedure isn't easy). If your growth plates are still open and your height is less than 2nd percentile, then a pediatric endocrinologist might be willing to evaluate you for possible growth hormone deficiency.

Not likely: I agree with dr. Lin. Unless you entered puberty late or have an endocrinologic problem, you are not likely to have further growth spurts in height. Good posture can help to maximize the height you do have.