No matter what, DO NOT re-bleach or try to strip your hair of color, this will only make things much much worse!
If store bought color is your only option, then just buy a rich, dark shade of brown, and that should cover and dull the red pretty decently. When it comes to store bought color, even the dark shades contain a degree of bleach in them, so it's not the
best option. If you do go with store bought, buy a good quality leave-in conditioner which you can use after the color treatment to counteract the damage that double processing with the dark color might do. Redkin can be found at most grocery/drug stores, and their leave-in treatments are salon quality.
As hunnychile said, if you can, you should go to a salon with a good reputation where they can fix the problem for you. The products that they use will be *much* easier on your hair, and they'll also have a better idea what shades to use to get you where back where you want to be. Red is the hardest color to work with, so you'll have a better success rate with a professional.
Good luck!
