Remove the door from the hinges. Lay the door across two sawhorses.
Apply a chemical paint or varnish stripper according to the manufacturer's recommendations. Some chemical strippers come as both paint and varnish removers. Chemical strippers are available as sprays, gels or liquids.
Allow the stripper to remain on the surface according to the manufacturer's directions, generally between 15 to 30 minutes. Natural strippers may take up to 60 minutes.
Scrape the paint or varnish off the surface with a plastic paint scraper.
Wash the door with detergent and water and dry thoroughly before reapplying a finish. Turn the door over and repeat.
Remove the door from the hinges and lay it across a stable work surface. Remove varnish with a chemical stripper and wash the door thoroughly.
Sand the surface of the door with fine-grit sandpaper to remove the layer of stain. Sand in the direction of the wood grain. Wipe the surface of the door with a tack rag to remove sanding dust. If the wood stain penetrated deeply into the wood bleaching is necessary. If that is the case with your door, move on to Step 3.
Apply a two-part hydrogen peroxide bleaching agent to the surface of the door. Technically, wood stains are not strippable; lightening with a strong solution of hydrogen peroxide and caustic soda will bleach the color. Allow the bleaching agent to remain on the surface according to the manufacturer's directions and the depth of color you are lightening.
Apply the neutralizing agent, usually included in a bleaching kit, to the door to stop the bleaching action. Wipe the bleach from the surface with a rag. Saturate a rag with white vinegar and wipe the door to remove bleaching residue. Turn the door over and repeat.