You can edit a device group to: add to the group; remove firewalls from the group; update friendly name and tags.
To edit a device group
The Root Group cannot be edited.
Navigate to Manager View | Firewalls > Groups.
In the Action field for the group you want to edit, select Edit Device Group.
Make changes to the Friendly Name and Tags fields, if needed.
To add devices to the group, select devices in the Unassigned Devices list and click the caret-right icon to move them to the In Group. To remove devices from the group, select the devices in In Group list and click the left-caret icon to move the devices to the Unassigned Devices list.
To move devices from one device group to another, first you need to delete the devices from one group and then add them to the other group from Unassigned Firewalls list.
When you add a device to a group that already has a template applied to it, the template configuration is made available to the newly added device and therefore you need to commit and deploy the available updates on to the device.