Based on the sort of question you're asking and the complexity, I think it'd be wise to seek out in person a trusted hairdresser whose expert in color changes.
Firstly, why would you take such a risk of messing it up by attempting it yourself?
Secondly, why would you trust total strangers with advice like this? I don't think that is a wise idea.
Lastly, I could be in error, but I know of no professional hair colorists here on A2K.