If you have set up your sudoers file and have a working sudo command (recommended), then simple issuing a `sudo programname from a terminal will allow you to run the program with root privileges. Since you’re looking for a file manager, you would use `sudo nautilus`, enter the root password and nautilus will opon up in /root with full access to all files/folders.
Ubuntu desktop users: If you’re constantly creating “sudo” sessions in Nautilus (or other applications), it’s very easy to confuse your sudo windows with your regular windows. This often results in accidentally opening read-only versions of your system files — very frustrating! A quick way to visually separate your simultaneous sessions, is to assign a different theme to your sudo applications. To do this, open a terminal and type the following:
Pick a new theme, and any time you launch an application using sudo, you will be able to clearly see the difference between your sudo windows and your regular windows. Check out the difference in the Nautilus sessions shown above (the sudo window is shown in brown on the right, and the regular user window is shown in blue on the left).