When you delete a device group, all the sub-groups also get deleted. All devices under the device group and its sub-groups will be automatically assigned to the parent group—Root Group.
When you delete a sub-group, all devices under the group are automatically assigned to its parent group or root group.
To delete a device group
Navigate to Manager View | Home > Firewalls > Groups page.
Click the Ellipses icon in the ACTION column of the group you want to delete, select Delete Device Group.
Click OK.
To delete multiple device groups
Navigate to Manager View | Home > Firewalls > Groups page.
Select check boxes of the groups to be deleted and click Delete on top of the table.