Sometimes when you click on the navigation list, the customize option may not be visible by default ( it is shown as read only)
This is similar to default smartlists. You cannot modify the * smartlists. You have to save favorite to save your modifications. Similarly, you need to create a copy of the navigation list using the Save As option.
Enter the name for the new view
Once a copy is saved the list is no longer visible as Read Only and you can customize it.
Use the List View Customization window to modify the content, layout, and sharing settings for a list view.
You mark the contents to display, Add/Remove columns, Customize Action Pane and select users with which you want to share the updated list.
Select the columns
You can select what you want to display and what not to display in the Action Pane. You can rearrange how various groups are displayed in Navigation List
You can also preview changes before saving them. And that’s it !!!