HELP!

I want to lighten my hair but Im not sure how i can achieve this;

So my hair has been previously dyed to black (it was lightened before) and right now I want to lighten it again. I have new growth thats like about 2 inches (my natural is dark brown). And the rest is blackish brown (wich is the dye). I know it will be tricky to get the overall lightened color since my hair is already previously dyed. What do i do to get the color i want without it being 2 different colors?