Okay, there is a stripper product on the market called ColourB4, but the problem is, you cannot redye it straight away as the colour will reoxidise and you will be back to where you started. It needs 7 days/3 washes in between (or 5 ish days minimum, so that's your working week)
You cannot "redye" with a lighter colour and expect it to lighten your hair - it doesn'tn work that way, you will just use up "conditioning points" or "9 lives" that you can't afford to lose.
Bleach will lighten it, and allow you to redye immeditately, but is harsh.
How dark is it? A bit too dark? A lot too dark?
You can just wash it 10 times tomorrow (in a row, one after the other, rinseing well in between!) and again on Monday morning. This will probably achieve something.
And is probably your best bet.
Or - if game - you could buy the Scott Cornwall foil effects cap, some 40 volume bleach, and a semi permenant colour of highlight you would like, and follow the instructions and add highlights to your existing colour to lighten and soften the overall effect.
They are the only options that will work.
Reply if you need more info.