How do you lighten dark dyed hair?

Either let it grow back out to your natural color, or bleach it. I would not recommend bleach, as this makes your hair very coarse and straw-like, especially if you dye it again after bleaching it. Also, colors that you dye on top of bleached hair often come out very bright and fade to strange, undesirable shades. Growing your hair back out is your best option.

If you JUST dyed your hair, give it a few weeks. The color should fade a little bit, and that color might be more acceptable to you.