How to reinstall Ubuntu 13.04 Raring Ringtail safely? [duplicate]
Note: Re-Installing should not affect any of your documents but, just to be on the safe side, you should do a backup of your documents, including /home hidden files, using something like CloneZilla
Boot your system from CD or bootable USB, and when you get to the installation screen, choose upgrade 13.04 with 13.04 if available, if not choose something else,
and when you get to the partitioning screen keep everything the same, and un-check the Format check-box.
For more info see the Ubuntu Reinstallation site
Source:Ubuntu Reinstallation