In order to manage availability, log into your account and navigate to Products > Scheduled Events/Unscheduled Events and click on the desired Event Image or Details in the Actions menu.

Choose the desired date you wish to edit by clicking in the calendar.  The activity’s Time Slots will populate.  From here you can close out the availability of the entire date, or you can click on a specific time slot to edit.  After clicking a specific time slot you can click Overrides to make edits to that whole day (or individual time slot's) capacity and pricing.