You can configure an existing user role by clicking an entry in the Roles Table. This displays the following dialog, allowing you to configure the role:
Users - allows users to be assigned or unassigned the role
To assign users to the role, click inside the blank space of the Users field and select a user in the drop-down. To add all available users, click Select All. To remove users from the role, click the "x" beside the user name. To remove all users, click Deselect All.