Try scoring the wallpaper first with a scoring tool.
Then try using Downy fabric softener full strength
applying it to the wall with a paint roller. Let the
paper stand for about 15 minutes to let the Downy start to soften the glue. Then try to remove the paper.
Let me know if this works for you. If it doesn't,
you can try vinegar in a spray bottle letting it set
for about 15 minutes after you soak the paper throughly.