Remove the previous covering on the staircase. Pull out old carpet and pry up the tack strips with a claw hammer. To remove old paint, apply a paint stripper according to the directions on the package, and scrape off the melted paint with a putty knife.
Sand the staircase with 150-grit sandpaper to remove any rough spots. Sand the stairs again with 220-grit sandpaper for a smooth finish. Follow the grain of the wood when sanding. Remove the dust with a tack cloth.
Apply a coat of oil-based primer to the staircase with a natural-fiber paintbrush. Follow the grain of the wood. Paint the treads and risers, and do not forget to paint the bottom of the tread if it has a lip that juts out over the riser.
Let the primer dry according to the package directions. Rinse the paintbrush in clean water. Open the can of oil-based interior paint and stir it with a paint stirrer.
Apply the paint to the staircase with a foam paintbrush, starting at the top of the stairs and working toward the bottom. Use even, overlapping strokes to apply the paint. Let the paint dry, and then apply a second coat. Wait 24 hours before using the stairs.