I am asian and my hair is black. Since it started turning grey, I have been dyeing it medium brown but it does not really look brown. I like it be a lot lighter brown. How do I go about it? What shade should I use? Or would it be better if I seek assistance from a professional in a salon?

Anytime you are removing color from the hair (stripping, usually with bleach) you need to seek the services of a professional. In my office alone, we have three at home bleach disaster stories. I bleached my hair black and orange once. In general, your current color will be stripped with bleach and then the color you want will be applied to the hair. You'll also want to keep in mind that going lighter all over is a great deal of maintenance.