Edit Style Sheet...
Edit Style Sheet lets you edit the style definitions for the current notebook.
Open the style sheet and modify the cell styles you want to change. Style changes will be reflected in all notebooks that use the style sheet.
If the notebook is using a shared style sheet, a dialog box will appear giving the following choices:
Import Private Copy
Copies the settings from the shared style sheet to a private style sheet just for this notebook. Any changes made to the style sheet will only affect this notebook.
Edit Shared Style Sheet
Opens the shared version of the style sheet. Any changes will affect all notebooks that refer to this style sheet.