Sanding is probably not the way. I've done the same thing on the top (only) of an oak table. I used diluted chlorx. You are, in effect, bleaching the wood. I had to experiment with the strength of the chlorx on a small spot. I made mine really strong because I wanted to remove the stain entirely. Not sure there is a way to "lighten" the stain. You might want to just bleach to before-stained state and re-stain the color you want. There are also some "stain" removers on the market--however, I tried one with no one. Chlorx worked well. Good luck!