[Alecsmith]

Hmmm there is not special upgrade method u can use simple step upload and overwrite all files with new one downloaded from members.vbulletin.com then run upgrade file using http://www.domainname.com/install/upgrade.php

But before u start upgrading check all currents mods are comfortable with new version and disable Mods globally from config.php by adding

define('DISABLE_HOOKS', true);

just under <?php

Main thing take backup of your forum before u start upgrading week ago i upgraded my board from Vbulletin 4.1.4 to 4.1.9 and its finished without any problem had some problem with template but i edited them