Pierce the wallpaper with careful horizontal slice marks using a box cutter. Start 2 feet below the top of the wallpaper and make a 3- to 4-inch slash in the wallpaper every 2 feet. Repeat this for every strip of wallpaper in the room to allow moisture to seep into the wallpaper and loosen the glue adhesive.
Pour 1/3 cup of liquid fabric softener into a spray bottle and add 2/3 cup of warm water. Shake the bottle to mix the solution. Spray the diluted fabric softener on the wallpaper until it's saturated. Allow the fabric softener solution to remain on the wallpaper for 15 minutes to help soften the glue.
Pry the upper corner of one wallpaper strip away from the wall with a plastic scraper. Once you've lifted enough to hold onto, grasp the corner with your fingers and pull the wallpaper strip down and away from the wall. If any pieces of wallpaper remain stuck to the wall, repeat steps 2 and 3 until they're removed.
Mix a 50/50 solution of white vinegar and water in a bucket. Wet a sponge with the solution before wringing it out. Wash the wallpaper adhesive off the walls with the vinegar solution. Use the plastic scraper to loosen any difficult-to-remove chunks of paste.
Dry the walls with clean cloths. Let the walls air dry for 24 hours before hanging new wallpaper or applying paint.