Note
You can ONLY edit personal calendars and group calendars which have been created by yourself.
For group calendars which are created by another users, you can ONLY edit them if you are granted the Edit permission. Meanwhile, for shared calendars, you cannot edit them. If you are granted the Edit permission on them by the calendar creators, you can ONLY have the right on their tasks or events (for example, adding/modifying/deleting, exporting/importing).
1. Hover your cursor over the calendar which you want to edit, then click 
that appears.
2. Click Edit from the drop-down menu. The form to edit the calendar will be different, depending on your selected calendar type. For example, if you select a personal calendar, the form only contains the Calendar Details tab.
3. Make changes on the calendar, then click Save to accept your changes.