To rename a group node, select the group node and click its Group 
icon to visualize the group network. In the group network view, select the group node, then in the ShaderfxShader Attribute Editor, replace the text in the Name field with the new name for your group.
To rename the categorization of the group node (Class name, Category name, Sub menu name) so that the marking menu item from which you create the group node is renamed, you must first resave the group with a new Class name, Category name, and/or Sub menu name, and then delete the old group. See Deleting a group for more information.