Important: If you want to update a group, simply upload the group with the changes (privacy, group type, description etc...) and it will update the group no action needed.
To manage your groups via CSV, simply format your CSV file the same as you would when creating a group, but add in an action column in the first column.
In the action column there are two codes you may enter:
Delete - This will remove the group entirely
Purge - This will remove all users except admins from the group
Once formatted, simply add to the groups' folder and it will be processed according to the action column.
Find a CSV template here...