Hey Feedom,
From the 'black color' I take it they are oak floors. Oak and moisture create black due to high tannin acid in wood. Miniwax makes a product called Renovator that when used with steel wool will dissolve old wax residue and may lighten stain. Wood bleach may also lighten area as mentioned. Sanding may take out stain depending on depth of color. Board replacement would be another option and not too difficult. Board would have to be sanded to match existing wood thickness, then finished. If floor has had nothing done to it recently then top coat is not protecting wood. Having been waxed it would need to be resanded and a new poly coat put on. If you have any questions feel free to PM.

Tim