For information on creating course groups, please see Creating and assigning groups.
If you want to update a group of courses by removing one or more course, substituting or adding more courses, changing the name or default duration between courses, you can do so easily under the 'groups' section of your administrative account
and click on the name of the group you want to edit, not the check box next to it. 
Change group name
Click "edit" next to the name of the group. The following page will allow you to change it as needed. You will not be able to change to a name that is already in use. That is, you cannot have two or more groups that have exactly the name name. You can have as many variations of group names as you want: "Office 1, Office 2, etc"
Change Course Duration
You can change the default duration between courses by click 'edit' next to the existing duration and selecting a new duration and clicking 'next'
You will be prompted to select whether this change will affect all users currently assigned the group or just those from this point on. Selecting to affect existing users cannot be undone once submitted. Also note that changing the default duration will not change any custom target dates that were assigned (see Creating and assigning groups for more informatiuon)
Adding Courses
To add a course, click the "Add Course" link at the bottom. You will be directed to the course search page. From there you can select one or more new courses to be added. 
Once added you will be asked whether this new course will be added to the group for all currently assigned users or just new ones from that point. Note: Adding a new course could change the status of a user from complete to in progress. This also cannot be done on a per user basis. 
Deleting Courses
You can remove one or more courses from a group by checking the box next to the course name and clicking 'delete'
You will again be asked to select if these changes will affect users already assigned.
You will also be asked, if you choose to affect all users, if those who are in progress on the deleted courses should be included. 
In this last case you could, for example, choose to remove an older version of a course from a group. If you choose "No" on the first question, only newly assigned users will be affected and will not see the deleted course in their account.
If you select 'yes', any completed copies of the course will remain in the user accounts but will no longer be associated with the group, and will not contribute towards the completion percentage of the group. If the deleted course has not yet been started, it will be removed entirely.
You can affect all assigned users but avoid those currently working on the deleted course by selecting "no" on the second question.