Under the manual upgrade instructions "From version 6.1 or earlier" it says "1. Your server must be running version 6.1 or later." ?
Also it does not actually say how to upgrade, it just lists pre-upgrade checks and then Post installation procedure.
On the Plugins tab under unRaid Server OS it shows an option to update from 6.0.1 to 6.5.3 but when I click on the update button I get the following error:
plugin: updating: unRAIDServer.plg
plugin: downloading: https://s3.amazonaws.com/dnld.lime-technology.com/stable/unRAIDServer-6.5.3-x86_64.zip ... done
plugin: downloading: https://s3.amazonaws.com/dnld.lime-technology.com/stable/unRAIDServer-6.5.3-x86_64.md5 ... done
wrong md5
plugin: run failed: /bin/bash retval: 1