How do I untar a file on a host that doesnt use cpanel only phpmyadmin?

I have a tar file that I have uploaded to my host(which happens to be godaddy), but I have found out that they will not untar the file for me or do they use cpanel, only phpmyadmin panel is used. How can I get this file to be untared. This is a very important file that is essential for my website, so this is something I need to get resolved, any help would be greatly appreciated.