There's no such option on the Devices tab.
However you can update the group by using the "Import devices" plugin.
Select Functions - Import Devices.
Select a group, File Type = List, and type the device numbers which you want to update, one device number per line. Then click "Import".
In the next screen, select "Existing devices" - "Override", and then click "Import".
Note that this action will clear the existing groups for each device.