This is how we renovate tired old staircases. First remove old carpeting and tack strips. Then, saw off the nosing of existing stair treads flush with the top of the risers, and cover the old worn risers with 1/8" white Masonite. Then purchase or fabricate new treads (these were made from pine veneered plywood with a half-round pine nosing, to match the original pine floors). Then, mix stain to match existing wood flooring and apply three coats polyurethane. Finally, install treads with generous amounts of construction adhesive with a few 18 gauge brad nails. We also moved the handrail from the wall to a newly-build custom bannister. A closet with original-style door was added under the staircase, along with a panelled lower stair wall.