Cut the staples off with a diagonal wire cutter. Pinch any remaining wire flush with the tongue. There should be some resistance to joining the tongues and grooves (that is normal). After getting the staples out of the way, passing them through a planer could make fast work of cleaning off the existing finish. A few boards as a test would tell you if that is a good idea or not.

I have reinstalled previously finished flooring and then just sanded it all to gain a new surface, but I have professional equipment and do that as my trade.