Disabuse means to free someone of a belief that is not true. Many teachers of health find that when they teach, they spend as much energy disabusing kids of false beliefs as they do giving them the facts.
Disabuse is often connected to the word notion or idea. In singing lessons, you must disabuse young singers of the idea that they can sing better by singing louder. In the first year of college, many people are disabused of the idea that the way they are is "normal," by meeting so many people who represent other ways to be.