I dyed my hair black about 2 weeks ago. Is there anything I can do that won't kill my hair but that can get it lighter? My hair is normally medium-dark brown.

Some permanent color can lighten the hair a few shades, but permanent color can make black hair orange or red. A hairstylist can use a high lift color to give you your desired color, minus the unwanted shades. But, if want you to go lighter than 3-4 shades, you will need to chemically strip the color from your hair, and you have to deposit the color you want to have.