I need to upgrade MySQL from version 5.0.51a to 5.0.83. Can someone tell me how to do that and if it will mess up any of the websites or ISPConfig that I have on there already? It's an issue with a joomla site and my test server has a newer version of MySQL than my production server.
Does your distribution's package manager offer 5.0.83? Anyway, before you upgrade, I'd make an SQL dump of your databases so that you have a backup in case something goes wrong: http://www.howtoforge.com/faq/6_3_en.html
You can check that here: http://packages.ubuntu.com/ But Feisty isn't maintained anymore; maybe you should upgrade (if this is possible at all after such a long time).
I can't tell. Make a backup before you try the upgrade (or even better, try it on a test system first).