How can I remove painted wall paper from plaster?

You're going to need a steamer. Score the wallpaper first , the entire room. Then grab the preheated steamer and slowly, patiently work section by section to loosen the adhesive . Complete each section before moving on to the next section . A light hand scraper may be needed. Do not apply too much pressure . You don't want to damage the plaster. Good luck !

Heat. Heat is definitely the trick. A steamer or even a hair dryer should loosen it up.

thunk this will be a hard job, I would try with steam

i have removed a lot of wallpaper and found that I had best luck with a pump garden sprayer water and fabric softener. Protect floor . Fill sprayer with warm water and about capful of softener. Start at top and spray about half the wall. The trick is to wait at least 20-30 minutes. Remove paper and do lower half . Also wash paste of walls because it will be softened and easier wash off. I always used a broad knife which is just a wide putty knife

I recommend renting a steamer. First score the paper, then steam. A broad plastic scraper will be your friend. The heat from the steamer should also make removing the paste easier. This is a long hot job. Good luck.