When lightening your hair, you must mix a developer--a creme containing peroxide--with your haircolor of choice. Developers come in different volumes; the higher the volume you use, the more you'll lift your dark haircolor. Developer is sold in 10, 20, and 30 volume forms. The 30-volume developer lightens the most and should be used when you want to go extremely light, while 10 volume lightens only a couple of levels.
Read the instructions carefully for the products that you purchase. Not all developers and haircolor kits are made equally, and not all haircolor kits are intended to be combined with a developer.
Slip on a pair of plastic gloves to protect your hands from the peroxide and hair dye chemicals.
Put a towel down over your work area if you are concerned about bleach damage. Put a towel around your shoulders when you begin to apply the product to your hair if you're wearing nice clothing.
Measure out two parts developer and one part hair dye with a measuring cup and mix them in a bowl.
Stir the mixture until the products are fully blended with the brush or applicator you plan to use on your hair.
Apply the mixture to your hair right after you are done stirring the two products together.
If you have dark hair, you may need to use a toner after this process to remove any orange or yellow tones your hair may develop.