Wash the hair
Red hair color can be one of the trickier shades to remove from hair, particularly if the natural hair color is light. Simply re-dying the hair doesn't usually work, as the red pigments tend to show through whatever color is placed over them. Before taking drastic measures, try washing the hair a few times with regular shampoo and hot water. If the hair color is a non-permanent variety, this should at least fade it. If regular shampoo doesn't cut it, try washing the hair with liquid dish soap that contains a moisturizer. Make sure to completely rinse the hair after using the dish soap, as it can damage the strands. Applying a solution of dandruff shampoo mixed with a tablespoon of baking soda can also fade color considerably. Simply wet down the hair, then apply the solution to the strands, making sure to rub it in thoroughly. Let the solution soak in for 15 to 30 minutes, then rinse.
Use an at-home color reversal kit
Color-reversal kits, available at drugstores and beauty supply stores, can remove hair color as long as the color problem isn't too severe. If washing the hair doesn't work, using an at-home kit is the most economical step. These kits generally contain a liquid solution that is applied to the dyed hair, then left on for a specific period of time. The solution removes the color pigments from the hair, stripping away the color. The downside to using color-reversal kits is that they can strip away the hair's natural color as well as the dye, leaving a dry, brassy or orangish head of hair behind. They also aren't salon-grade kits and therefore sometimes fail to completely remove the hair color. That type of damage requires another dye job to correct. When re-dying the hair, be sure to choose a shade that's close to to natural hair color and very gentle.
Visit a salon
If the previous steps fail, the best thing to do is visit a hair stylist at a professional salon. The stylist can chemically strip the hair of the red coloring and then re-dye the strands, adding highlights and lowlights to make the color look more natural. The stylist will also be able to apply a deep-conditioning treatment to the hair and recommend a hair-care regimen for the strands. This treatment severely damages the hair and shouldn't be used unless all other avenues are exhausted.