How do I add the "up one level" button to the Windows Explorer toolbar?
The functionality of the up one level button has been superceded by the new breadcrumb bar in Windows Explorer (shown below). You cannot add the up one level button to the toolbar.
You can click on any element in the breadcrumb bar to easily go up one, two, or more levels in a single click.
For example, if you are looking inside the Windows folder, you can click on "Local Disk (C:)" to go up one level, or you can click on "Computer" to go up two levels.
For even more versatility, you can click on the arrows between elements on the breadcrumb bar to quickly navigate to a subfolder of that element.
For example, clicking the arrow to the right of "Local Disk (C:)" will allow you to navigate to one of the folders contained in that drive, Program Files for instance.
You can still press the ALT key and the UP key at the same time to go up one level.