To remove individual light fixtures from a lighting group, go to
Ribbon: DM Electrical->Lighting Groups-> 
Remove Lights from Groups
Pulldown Menu: DM Electrical->Lighting Groups->Remove Lights from Groups
You will be prompted to identify which light fixtures are to be removed from a lighting group.
Select objects:
The selected light fixtures will be removed from the lighting group and the lighting group labels will be removed from the light fixtures.