This is a calendar event. To edit it, browse to the slug in the Control Panel. You can edit this content in the Intro tab under 'Event settings.' Other details about the event, such as the location, date, and the Autoresponse message sent to attendees can also be edited under 'Event settings.'
New calendar events can be added to calendar pages. This calendar is called 'events.' Create a new event by browsing to the calendar in the Control Panel and click 'New event' under the 'Events & subpages' tab. You can manage existing events here as well.