I am 21 and my height is 5'8 .. how to increase my height? ?

Nature determines Ht: Most people reach their maximum height in their late teens. Without nutritional problems or chronic childhood illnesses, height is largely based on genetics and parental heights. Aside from eating right, exercising, sleeping well, and being happy all throughout childhood, there's not much a person nor his doctor can do to increase height. 5' 8" is a normal height for men anywhere in the world.