Clear all movable items from the room and clean the floor. Dust or sweep the area with a clean cloth to remove as much dirt and dust as possible.
Apply chemical stripper to the floor. Use a paintbrush to apply a uniform coat of the stripper to all areas of the floor. Be careful around corners, being sure to get the corners without touching the walls.
Scrape the polyurethane off. After the chemical stripper has set the manufacturer's recommended amount of time, the polyurethane will begin to bubble and turn loose. Use a putty or floor scraper to remove from the floor. Collect and dispose of the scrapings.
Sand the floor lightly to remove any remaining polyurethane. Small bits may stick even after stripping. Lightly hand sand these areas to get any remaining bits.
Sweep or wipe down the floor to get rid of any remaining loose debris.