[otrs] Upgrade query

Good afternoon, I have recently been tasked with upgrading OTRS from a rather old version (3.1.11) to the latest version. I have access to the old server, plus I have stood up a brand new CentOS VM for the new installation. I cannot find any information online about performing such a large upgrade, and wondered whether anyone here could point me to a resource (or if not, could provide assistance). Thank you very much. Pete