How do you lighten hair color after alreeady applying it?

There are only two ways of lightening haircolor. You can use an at home product such as ColorFix, that will remove permanent hair color but will leave your hair in a "bleached or raw" state and you can then reapply the color you want or tone. The other way is to straight bleach your hair (using a hair lightening product of some kind) and then basically again it will be really for color or toning. Both of which can be a disaster if you don't really know what you are doing. So the recommendation is to always seek a professional, they can either do the process for you or maybe just a color correction would be needed.

If you want to go lighter or blonde, you will need to bleach your hair and then deposit the desired hair color. Anything other than that will result in orange or brassy shade.