Color Strip and re die. But You are going to want to wait a few days from your first coloring to do the color strip becuase of how harsh it is to your hair.
try stripping it 1st. its like bleaching only less harmful to the hair, then use a dyeing kit to make it the exact color you want. use a lot of conditioner and don't dye it for a wile after that. my sister did the same thing and did this and it worked. good luck =]