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 on the Properties panel, replace the text in the Name field with the new name for your group.
Important: Strings that you enter in the ShaderFX editor, such as node names and group names, must contain only ASCII characters. Unicode characters are not supported.
To rename the categorization of the group node (Class name, Category name, Sub menu name) so that the right-click menu item from which you create the group node is renamed, you must first resave the group with a new Class name, Category name, or Sub menu name, and then delete the old group. See Deleting a Group for more information.