The first step in any remodeling project is removing old paint and polyurethane from any wooden surfaces you want to refinish. With a little effort and care, you can easily remove the old paint and polyurethane from any wooden surface to ready it for refinishing. Apply the chemical paint stripper to the paint and polyurethane on the wood surface. Wait until the paint and polyurethane begin to bubble and peel. Scrape the paint and polyurethane off with the plastic putty knife. Don't use a metal scraper as it will damage the wood. Wash the wood with a damp, clean cloth. Do this to remove any excess paint stripper to prevent any damage to the wood surface. Sand the wood with the 400-grit sandpaper. This will remove any last bits of old paint and polyurethane and give you a clean, smooth wood surface to work on. Sweep any dust and debris with the broom. Make sure the wood surface is clean before reapplying any new coats of paint or polyurethane.