How do I unsubscribe from a calendar (i.e. delete a calendar subscription)?

Open Windows 10 Calendar application.

On the left you'll see a list of calendars.

If the list is closed, click to expand it.

Note that you may have more than one group, depending on how many accounts you have configured.

A list opens. It shows the calendars under that account.

Move the pointer on top of the calendar you wish to remove.

A appears. Click it to open a menu.

On the menu that opens, click Remove calendar.

On the confirmation dialog, click Continue.