actually you can... just use peroxide and after that you should use stuff from La riche Directions, Manic Panic en Fudge. But you are best off to go to a hairdresser
Ma'am, You tempt me to try
Leana is right about it being possible, but let me warn you still... It depends ALOT on your hair-quality and natural colour.
You will have to bleach your hair at least three times to get it whitish, and if your hair isn't in extremely good condition, there is a risk that it breaks. (Bleach strips off a layer of your hair and opens it. If you do this too often your hair will become so thin and weak that it breaks and falls off.)
So the best way would be to bleach once, wait a week whilst using conditioning products ALOT, bleach again, wait a week, repeate.
Also, if you have naturally lots of red pigments in your hair (like me) the bleach won't be able to strip that off very easily, so even after three bleaches your hair may look... Yellow. This unfortunately can't be fixed by bleaching yet again, but you can use a silver- or blue-toner and shampoo to even out the yellow. Your hair will look greyish at first, but it'll get evened out eventually.
Unfortunately, toner and tint-shampoo is something you have to repeat often. Shampoo every time you wash, and toner about every second week, to keep it good.
White hair is a hassle.