First of all, what do you mean by whiten your eyes? The white portion of your eyes is known as the sclera, and the fact that yours are discolored can mean several different things. The best advice I can give you is that you should go see your family physician
to evaluate you who may refer you to an ophthalmologist.
The color of the sclera of your eyes can actually mean different things. If your eyes are bloodshot [red, with vessels prominent] it could mean that you are simply stressed and not receiving enough sleep. You can resolve this issue simply by getting more rest.
If your eyes are "yellow" in color, this could indicate that there is something wrong with your liver or biliary system. Sometimes, when patient's have issues with either of these systems they get a build up of what is known as bilirubin - which can lead to the yellowed appearance of your sclera/eyes. Most patients with this problem also have the underneath portion of their tongues [frenulum] yellow in color.
A third possibility is that you may have a disorder known as osteogenesis imperfecta - which is a disorder in your connective tissue, and is commonly known as "Brittle bone disease". If the color of your sclera is blue, you may have this issue.
The best thing to do is go to your family physician and ask him about this issue. The color of your sclera/eyes can actually tell you if something is wrong - and by fixing the problem you can usually resolve the discoloration in your eyes.