Hair color removers all work by shrinking the color molecule contained in artificial hair dyes. Then you can recolor with a new dye.
They are great for having black hair, multi-colored hair, red hair, or any stubborn color and will give you a base color to work off of.

They should not be used to go just a few shades lighter or darker!
Hair color removers are harsh and can potentially fry and break your hair during processing!
Do not use them if you have permed, bleached, or have any other type of hair damage.

If your hair is way past shoulder length, you'll probably need 2 boxes. You can purchase Hair Color Removers from almost any grocery store that sells hair dye (USA), they generally cost about $10.00 to $12.00 (USD).
Please follow all instructions within box.

It's best to wait a day after using a hair color remover before applying new color.
Please keep in mind your hair color after using a hair color remover can effect your results of your next dye.

For example, you will probably have a brassy hair color after using a hair color remover, adding a cool toned color, such as dark blonde, will most likely give you a dark reddish blonde hue.