Load the buffer with a medium refinishing screen. Start the machine. Run it over the floor in the direction of the boards, moving it forward and back. It should remove most of the existing gloss.
Vacuum up the dust. Reload the buffer with its fine screen. Run it over the floor again, taking up the last of the old gloss. Vacuum the dust.
Brush on a coat of polyurethane gloss with a paintbrush, starting at the furthest corner of the room from the entrance. Use light, even strokes, going with the direction of the floorboards.
Let the polyurethane set for eight hours. Hand sand it with extra-fine sandpaper to remove the glossy surface so the next coat will adhere. Vacuum the dust.
Apply a second coat of polyurethane in the same manner as the first. Let it dry eight hours. Hand sand. Vacuum. Apply a third coat. Let it set for 24 hours.