How can you get weed out your hair?

You can't. As the hair grows out, the chemicals in the marijuana are in the hair shafts, and can't be washed out or removed with any internal cleansers. The only thing you can do is to stop using marijuana, then cut your hair. And since hair grows on average about 1/2 inch per month, you would have to shave your head, or wait until you've gone a few months without smoking it and then cut it very short.