There are two options to handle upgrades from waitlists in the LMS: automatic and manual.
Automatic Waitlist Handling
The Automatic Upgrade option puts the LMS in charge of handling a course's waitlist. Learners are placed into pending approval status until the end of the enrollment period, at which point the LMS checks whether the registered number of enrollments exceeds the minimum class size. If it does, the learners are enrolled or waitlisted on a first-come first-served basis. Enrolled users receive enrollment confirmation emails and the course is displayed on their My Courses page. Waitlisted users are either withdrawn by the LMS or transferred to another session of the course (if configured by the administrator).
Manual Waitlist Handling
The Manual (Administrator) Upgrade options allows the administrator to change the learners' status (from Waitlisted to Enrolled, for example). Learners can check their status under the Pending Enrollments menu. Notification emails are sent to confirm enrollment and the course is shown on their My Courses list once they are approved.
To automatically clean up waitlists once the enrollment period is over or the session has started, enable the Clean-up waitlist automatically System Configuration setting. The LMS will set the overall status of waitlisted users to Dropped from Waitlist. You can configure the Dropped from Waitlist Notification in the learning module's Email Preferences Setup. The notification will be sent to the learners who have been dropped from the waitlist either automatically or manually.