I am 18 years any my height is 4'11 how to improve my height?

Once your growth plates in the bones close you will generally not grow any taller. Most females reach their full adult height between the ages of 14 & 16. Sometimes there may be an increase in height until about 19 yo with good nutrition, adequate rest & exercise. Keeping a good posture & elevator shoes can help you increase your height. I wish you well with your health!