I’ve configured my Outlook.com account in Outlook and here I see multiple Calendars like my default Calendar, a Birthday Calendar, a Holidays Calendar and a few more I created.

Now I want to delete the ones I created as I either copied the items to my main Calendar or simply no longer need them. However, when I right click on the Calendar in Outlook, the option to delete the Calendar is greyed out.

How do I delete these Outlook.com Calendars?