How to lighten hardwood floors in traffic area?

It appears it need a deep cleaning. First remove all debris and dirt that is loose: sweep, dust mop, swiffer, vacuum - whatever works best. Then deep clean by mixing 1 cup apple cider vinegar, 1 Tbsp blue Dawn, 1 gallon HOT water. Wring mop and scrub in the direction of the floor. For normal mopping up the water to 2 gallons.

Use a mixture of baking soda and toothpaste.

1. Put the mixture onto a damp cloth and rub with the grain until the stain is gone.
2. Clean the area by washing with oil soap.
3. If the stain doesn't disappear the first time, try another application.

If you can't get the stains off, you could switch boards. We had some boards under our refrigerator and we swapped them with some boards in a high traffic area and it worked out great.

Try a product called Rejuvenate for wood - works great! But your best option for a worn out wood floor is to sand and refinish

If you're eventually going to sand and refinish or replace, you could use very wet magic sponges to remove the ground in dirt. Be careful because it could take off some finish . I did this carefully and it came out good, staving off an immediate repair.

I agree with Sandy OToole. Those magic erasers do a great job. I use the heavy duty ones, by Mr Clean. bought at Home Depot, but I'm sure they are everywhere. Buy the big box, you will need every last one of them. I don't know what makes them work, but by golly, they clean everything! They do disintegrate, but you can get a lot of use out of each one, just be sure to constantly rinse them out and they will work wonders on your floor.