You searched for: “lessen
lessen, lesson
lessen (LES uhn) (verb)
To make smaller or to reduce, to diminish: The medication the doctor gave Mable will lessen the pain of her sprained ankle.
lesson (LES uhn) (noun)
1. An excerpt from sacred writings read as part of a religious service or ceremony: The child read the lesson for the morning in a clear voice.
2. An assignment, exercise, or task to be studied and learned by a pupil: It is time for Billy to practice his music lesson.

The teacher wanted to decrease the content of her next class presentation; so, she told her students that she will lessen the next lesson.