Click Edit > Copy by Family.
The Select Copy Family dialog box displays.
Select the family to modify under the Copy Symmetry Families hierarchy.
Click Edit Family Definition in the Select Copy Family dialog box.
The Symmetry Family Properties dialog box displays.
Using the dialog box controls, edit the family as needed.
An existing coordinate system in the Symmetry Planes box cannot be deleted. You can delete the family in the Select Copy Family dialog box and create a new one with the needed coordinate system.