The first thing you should do is determine the type of wallpaper you have. If the wallpaper is water-sensitive, such as vinyl or foil-coated, use a non-abrasive cleaner or detergent mixed with warm water and apply with a soft cloth. If the wallpaper is washable or stain-resistant, gently scrub with a sponge soaked in mixture.

Once the majority of chocolate has been removed, use a household cleaner to dissolve any remaining residue. Apply cleaner onto a damp cloth and press it onto the stain. Let the cloth sit for a few minutes and then carefully blot away solution with a clean cloth. To further protect the wallpaper, you could then rinse area with cold water.

You can also try using white vinegar and water to remove chocolate stains. Mix together one part white vinegar and one part water in a spray bottle. Spray affected area and then blot with a cloth. This method is best used on non-washable wallpaper.

No matter what type of wallpaper you have, it's important to test any cleaning solution on an inconspicuous area first. Always work in small areas at a time so that the wallpaper won't become overly wet. And if the stain still won't come off, call a professional.