You downloaded Joomla as a RAR file? First of all, delete the file and go to to download the newest version of Joomla. Whatever you have is not an official release and I would not trust it.
Most likely, cPanel will only be able to extract files that are .zip, .gz, .bz2, or .tgz. Do you know if your host provider is using Linux or Windows for hosting? If Linux (or another UNIX variant) I would download the .bz2 file from Joomla’s site. If Windows, chose the .zip.