Anonymous
Yep a steamer is the answer. Wallpaper steamers are very effective and not very expensive. As it has been painted you may need to briefly wire brush the wall so the steam can penetrate. But try without first.
Ghost Of Christmas Past
If it's emulsion paint, a steamer will shift it. You can hire them although they don't cost much to buy. If it's oil-based paint, you should be able to peel it off. You may find that the paint comes away and leaves some of the paper, but you can get rid of that by soaking and scraping.
Penny
Steam iron sometimes works to loosen the paper. If you are exceptionally lucky, the wallpaper will just come off in strips. More often you will need to tediously scrap with flexible putty knife.
Anonymous
Check out venetian plaster! Put it on top of wallpaper.
rnsbrz
It should just peal off now, but you may have to steam it off. Try scraping off first, then use a steamer if it becomes necessary.