You can color lighter hair dark quite easily because you are simply putting pigment onto the hair. Lifting hair color that is too dark, however, can be much more of a challenge. In order to lighten dark hair you must do a color correction, which involves bleaching the hair pigments and toning or dying the hair to the desired shade. This can cause extensive damage to the hair shaft, leaving your hair looking fried and brittle, not to mention cost you hundreds of dollars if you go to a salon. You can lift hair color that is too dark at home with safer, less expensive color correction methods, but you must tread carefully to avoid damaging your hair further.
Wash your hair with an anti-dandruff shampoo. These shampoos are stronger than others and help to clarify the hair, stripping it slightly and helping to remove dye.
Massage dish soap into your hair, allow it to sit for 15 to 20 minutes and then rinse off. Dish soap is quite harsh to the hair so you do not want to leave it on for too long or repeat this process too often, but it can help lift color that is too dark from your hair.
Dye your hair with an ashy brown or blond color. This helps remove red tones in the hair and bring the color to a lighter, brighter shade. Although this will not lift the dark color completely, it does lift it slightly and the lighter colors make your hair appear much lighter overall than it actually is.
Coloring hair, in general—but especially harsh processes such as color corrections—can damage the hair. To help nourish and revive your hair, as well as protect it from future damage, apply a deep conditioning treatment to your hair once every two to three weeks.
If your hair is really a disaster or needs to be lifted more than three shades, you may be better off visiting a trained hairstylist for a professional color correction. They have more advanced tools and products than you can find in stores and have the knowledge to understand how to properly lighten your hair without having it turn any strange, unwanted colors.