Office 365 (Outlook 2013 / 2016 / 2019 for Win) - Change Permission Levels Once You Have Shared Your Calendar
In the toolbar at the bottom, click Calendar. ***NOTE - Starting with Outlook 2016, icons have replaced words if you have Compact Navigation enabled. If so, click on the calendar icon.
Within the Home tab, select Calendar Permissions.
Select the name of the person whose permissions you would like to make any changes to. Please reference the chart at the end of this article for more information about what the various permission levels mean. Please note that the various permission options change based on the Permission Level that is selected. Once you have made your selections, click OK.