Soak a sponge or paint roller in hot water. Liberally rub or roll the water on a small area, such as a 3-foot by 5-foot section. Wait about two minutes for the water to soak in, then score the area with a wallpaper scoring tool, which has a set of teeth that punch tiny holes in the paper to make removal easier. Scrape with a scraper or putty knife. Do not press or scrape so hard that you gouge the wall. It may take one or two sections to figure out how large an area to soak, in which direction to scrape and how hard to press.
Instead of plain hot water, add 1 cup of white vinegar to every gallon of hot water. If hot water alone works well to remove most of the wallpaper, use this solution for areas that are harder to remove. Then wipe the walls down with a solution of water and vinegar to rinse them.
Wallpaper streamers are available for purchase or rental, but you can also use steamers typically used for fabrics. Because they are small and need lots of refills, using a fabric steamer will be a time consuming process, but should help remove the wallpaper. Hold the steamer close to the surface of the wall without touching and slowly apply steam to a 3-foot by 5-foot section. Then score the wallpaper and scrape. Clean the residue off with hot water or the vinegar mixture. You can also try scoring the wallpaper first to help the steam reach the glue.