The first thing you need to understand is that once hair is colored, it contains artificial pigment. Artificial pigment cannot be lightened using another, lighter haircoloring. You can darken it (deposit more dark pigment), but you cannot lighten it. This is why color removers were invented.
There are two types of color removers: Bleaching (oxidizing) agents and reducing agents. Reducing agents dissolve the artificial pigment so that it can be washed out. Oxidizing agents try to lighten the artificial pigment. Oxidizing agents don't always work and if you try and fail to get the hair light enough, you're out of luck (you can't try an oxidizing agent followed by a reducing agent -- it won't work). Reducing agents are less damaging to the hair. Reducing-type color removers include ColorFix, Color Oops and Igora Phantom. Color Zap and Effasol are oxidizing agents. For your information, here are some instructions for using ColorFix: Hair Color, Hair Care and The No More Bad Hair Days Kit by Robert Craig Salon Products, Ltd.
So, the first step is to use color remover to remove the black/brown dye. The next step, if you get all of that out, is to use a new dye to try to get the color you want. If the hair isn't light enough after using color remover (hopefully all or almost all of the artificial pigment is out), you have to bleach to get it to the level
you wish and then you dye it (tone it). Your natural color is quite dark so if you wish to get lighter than a level 4 or 5, you'll have to do some bleaching (a light shade of haircoloring won't work).
Using a light shade of haircoloring over colored hair is a recipe for damaging hair -- nothing more.