To remove wallpaper from plaster walls, start by scoring the wallpaper with a scoring tool or sandpaper to allow the removal solution to penetrate. Apply a wallpaper removal solution or a mixture of warm water and vinegar, and let it soak for a few minutes. Then, use a scraper or putty knife to gently peel off the wallpaper, working from the edges. Clean the walls thoroughly and allow them to dry before proceeding with any further renovation.