Office 365 (Outlook 2013 / 2016 for Win) - Change Permission Levels Once you have Shared your Calendar
In the toolbar at the bottom, click Calendar. ***NOTE - In Outlook 2016, icons have replaced the words as per the second image below.
Click Home > Calendar Permissions.
On the Permissions tab, make any changes to the calendar sharing permissions. Please reference the chart at the end of this article for more information about what the various permission levels mean. Click OK.