To make changes to your session, navigate to the 'My Sessions' section on the community tab, and press Edit on the event.
What you can change :
The name and description of the session
The session agenda and session length (via the agenda)
The maximum number of participants (only before the session starts)
What you cannot change:
The start time and date of the session. If you need the session at a different time, you will need to cancel this one and create a new session.
How to cancel a session
If you need to cancel the session entirely:
Go to My Sessions in the Community tab.
Find your session and press Edit.
Scroll down and click the Cancel button at the bottom of the page.
Once cancelled, the session will be removed from the public Community Calendar so people will no longer see or be able to join it.