I had my hair two toned and the underneath part of my hair is suppose to be dark brown and it looks black to me and I don't like is there a way to lighten it without damaging my hair?

I really love that two toned look and it may be a matter of perspective why it looks black to you. Go back to the salon. They may be able to lighten it for you safely, but I imagine you just have not got used to the contrast yet and should give it more time.

It will fade into a brown if you wash your hair with a deep cleansing shampoo.
Once you get the desired colour, start using a colour protecting shampoo. :)