It depends on why it is dark. Varnish, for example, often darkens with
age and is easily removed. If it is a dark wood, and you can remove all
finish, it can be bleached. If it is stained, that is more of a
problem, as stain usually does not soak into the wood to a uniform
depth, so you may sand, but only remove the stain on some areas of the
floor, leaving a rather mottled look.

I would suggest you find an area that doesn't show (closets are ideal)
and try a small area and see what kind of results you get.

wrote:
If you have a hardwood floor that has a relatively dark color, is it
possible to sand it, then restain with a much lighter color? I guess
the question boils down to how far into the wood the stain typically
penetrates? The floor in question is solid, not engineered.