Load the floor buffer with a medium refinishing screen. Start the buffer, and move it over the entire floor in a forward-and-back motion in the direction of the floorboards. The screen will remove the top coat of the gloss finish.
Vacuum the floor to clean up the dust.
Reload the floor buffer with a fine refinishing screen. Screen the floor again as before, getting it smooth and flat, and then vacuum.
Brush on a coat of polyurethane with a paintbrush in the direction of the floor boards. Make the layer thin and smooth, and cover the whole floor.
Let the polyurethane dry for 24 hours. Sand by hand with extra-fine sandpaper to dull the surface, and then vacuum the dust.
Brush on a second layer of polyurethane in the same manner as the first coat. Let it set for 24 hours.
Degloss the second layer of polyurethane as before, with extra-fine sandpaper. Then, vacuum. Brush on a third coat, and let it dry for 48 hours.