Change time, instructor, room, or cancel — apply to one session, this and all future, or the entire series.
Open the Schedule page (Day / Week / Month / List view) and click the session you want to edit.
For recurring sessions, pick This session only, This and all future sessions, or All sessions in this series. The dialog shows live "affects N sessions, M bookings" hints, and the Save button label updates to match ("Apply to 12 sessions").
Change start time and the end time follows automatically (Google Calendar–style). Use the Instructor picker to assign a substitute. The dialog warns in amber if the new instructor is already teaching at the same time, in red if the room conflicts.
When the change touches date, time, or instructor, the "Email confirmed members" checkbox appears (default ON). Uncheck for silent fixes — typo corrections or data cleanups.
Click Cancel session. The confirm row has an optional Reason field ("Instructor sick", "Snow day"). The reason saves with the session and shows on the cancelled tile so the next person knows what happened.