To quickly edit the permission levels assigned to Managers of courses or groups, click on People, then on Users, then click on the Manager that you want to edit.
Next, click on the Manager Permissions tab in their profile.
From there, you can quickly Assign them as a Manager of any Groups or Courses, remove them from ones they are already assigned to, and also edit their permissions.
If you click on the Permissions box next to each course or group that they are a Manager of, you can customize the level of access that they have for each specific group or course.
For example, here are the different permissions that you can choose to assign to a Group Manager:
Similarly, here are the different permissions you can assign to a Course Manager:
Check off each permission that you want to assign to that Manager and then click Save changes.
The various levels of permissions can be set differently for every Manager, and be customized across the different groups or courses that they have been assigned to manage.