I am now 20 years old and 5ft 5in tall. i want to grow taller, how am i support to do?

Limited: You are often limited by your genetics, but a balanced diet and exercize are your best bets!

Growth very unlikely: A 20 yr old is not growing taller if his growth plates have fused. If not fused, he will grow a tiny bit (pediatrician's growth chart for him can tell if growth has stopped). To look taller, one can choose properly designed clothing; shoes, and have good posture. Vitamins, supplements, "special" foods, extra exercise, etc... will not make a person taller if he already closed his growth plates.

Finished puberty: During puberty, you go through a growth spurt, then your bone growth plates fuse, and you stop growing. Unless you had a very delayed puberty, it is likely that you have finished growing.