How can i increase my height if i m 20 years old?

You can't...: You're almost certainly done growing, and even if you weren't because of delayed puberty, there's nothing you'd be able to do to change your height.

Platform shoes: Some kids continue to grow taller into their late teens or rarely early twenties but only when their bone maturity lags behind their age. If the growth centers of the long bones have fused, you cannot grow taller. A single x-ray of the wrist/ hand can yield a bone maturity. When you have reached bony maturity, you are done.No exercise, meds or diet will change that.