The accounting period cannot be deleted by the user. If you need to delete an accounting period or edit the same, you can send an email to firstname.lastname@example.org for action.
To add you own accounting period, go to the menu ‘Accounts -> Accounting Periods’. On this page, all the existing accounting periods are listed. The button ‘Add Accounting Period’ will take to a form to provide the ‘Start Date’ and ‘End Date’ for the accounting period. You will not be able to create accounting period which overlaps with an existing accounting period.