You can cancel your subscription at any time from your Profile page.
Head to you profile page at https://app.lessonmate.org/profile
Then scroll to the bottom to cancel:
We'd love to hear your reasons for cancelling so we can make improvements to LessonMate. It's not required but every bit of feedback helps!
Details on what happens after you cancel here: http://help.lessonmate.org/en/articles/5392847-what-happens-after-i-cancel