Emma, how strong of an auburn, how light?
If you're able, I'd do the color extractor as discussed in the dye or not to dye thread.
If not, and you don't want a very "light" shade, just "strong", I'd do a "bleach soap cap". Mix some bleach with some shampoo and water, shampoo into WET hair and let sit a few minutes, watch closely. This should pull up some of the color enough without going overboard. Regardless, your hair will feel different so have some good conditioner on hand.
If you can, I'd wait a day before applying the red overtop, it will hold better.
Keep us posted!