Add An Up Button To Pantheon-Files

Default look of Pantheon-Files with Backward and Forward buttons :

To add an Up button to the toolbar of Pantheon-Files we need dconf Editor.
You can install it by opening a Terminal and typing the following command :

sudo apt-get install dconf-tools

Start dconf Editor and go to  org > pantheon > files > preferences and look for toolbar-items in the right pane :

['Back', 'Forward', 'ViewSwitcher', 'LocationEntry']

Change into ['Back', 'Forward', 'Up', 'ViewSwitcher', 'LocationEntry']

Restart Pantheon-Files :