Patience and more patience. Use Dif wallpaper remover with hot water . Spray it on, let it soak in for at least 15 min.,keep wet and scrape with a putty knife. Work in small areas at a time. Try to peal off any protective coating on wallpaper so you expose the backing.
The drywall should have a coat of primer and 1 coat of paint. Then use a spray bottle and soak it with warm water. Use a spatula and scrape off the wallpaper. If it doesn’t have primer and paint I don’t know what would work. Probably nothing as it would take off the paper on the drywall.
Both answers are right. There are several removal products out there that work well. To speed it up you can get a tool that will score or poke small holes it the wallpaper. I recommend a plastic scraper, less chance of gouging the drywall. Mike is correct about the paint. If the drywall was installed correctly, it should have either 2 coats primer or 1 primer/1 paint. If the wallpaper was put on unprimed drywall, it won't come off with out damaging the drywall and will have to be replaced also.
Steam. It will peel right off with steam. I rented a steamer, but this is a good excuse to purchase a clothing steamer. Don’t waste money on Dif, soaking takes forever, use a steamer.