You need to take up all the carpets and make sure no floorboards need replacing. If they do you can go to scrap merchants that will sell you reclaimed boards (measure them to get right ones ie width). Then you need to hire sanders - a roller style one for main area and also edge sander for edges and corners. You also need masks when you sand - otherwise you'll choke to death on sawdust! Then you need to stain the boards to colour them.. Finally you need to varnish the boards with very heavy duty varnish for protection. All in all a few hundred quid... Its probably worth doing if they are Victorian floorboards - youd never get that quality of workmanship now.