Don't paint on wallpaper. Its pattern is hard to cover, and after aging, the wallpaper will peel off, together with your paint. It's easy to remove the wallpaper. The key is to soak then scratch. Because normally wallpaper surface is water-resistant, you either need to tear off its surface first, or use a tool to punch small holes so the water can soak in. HD sells the plastic punch tool that won't hurt your drywall. After removing the wallpaper, try to clean out the glue underneath as much as you can. Soaks with warm water, wipe it clean.