The iCal Calendar can get full of events that you no longer need, or perhaps a specific calendar you subscribe to makes it confusing to find the appointments that matter. You can delete events on your calendar only on a monthly basis, or you can also just delete the calendar completely, and then re-add it as a blank calendar.
Launch the Calendar application located in the Dock.
Click the "Calendars" button to show the sidebar.
Uncheck any calendars with events that you don't want to clear. Leave only the calendar you want to clear checked.
Click the "Month" tab. Select the "Edit" menu and choose "Delete" to remove the events permanently. Otherwise, select "Cut" to clear the events and copy them to the clipboard so that you can paste the events into an external program. Complete this process for each month you want to clear.
Information in this article applies to iOS 6. It may vary slightly or significantly with other versions or products.
You can also delete any calendar from the sidebar by right-clicking the calendar and selecting the "Delete" option from the drop-down menu. Confirm you want to delete the calendar by clicking the "Delete" button.
Clear the events to prevent the details from showing up in your calendar by unchecking the box next to the calendar you want to hide. This hides the events without deleting them from your calendar.
You can't clear events, such as birthdays, related to your contacts. To clear information stored in your Contact book that displays on the calendar, you must open the contacts card by right-clicking on the contact's event. Click the "Edit" button and press the "-" button next to the information you want to remove.