iCloud: Delete a calendar
When you delete a calendar from your Calendars list, all events associated with the calendar are also deleted.
You can’t delete all of the calendars in the list because it must always contain at least one calendar.
WARNING: When you delete a calendar, it’s deleted from every device that has the iCloud Calendar feature turned on. For example, if your iPhone and Mac have iCloud Calendar turned on and you delete a calendar in the Calendar app on iCloud.com, the calendar is also deleted in the Calendar app on your iPhone and Mac.
Click Edit below the sidebar.
Click the Delete button to the right of the calendar’s name, then click Delete.
If you accidentally deleted iCloud calendars or events, you can use iCloud.com to restore them, together with your reminders, from an earlier version that was automatically archived in iCloud. For instructions, see Restore your contacts, calendars and reminders, or bookmarks.