Safe upgrade routine for Cassandra

I've been tasked with upgrading an Ubuntu based Cassandra cluster - having no prior experience with Cassandra. I've tried digging through the docs but have been unable to find any instructions on how to do upgrades in a supported manner. Luckily I have a test cluster which upgrades fine by just ensuring that apt points to the correct repo and doing apt upgrade - but perhaps that is just due to the database not being under any particular load. Should the nodes be cordoned prior to upgrade or something similar? Or is it safe to trust apt to do its thing? Should, for instance, nodetool upgradesstables be run manually after an upgrade from 4.0 to 4.1? Is there documentation on this topic that I've failed to locate? I managed to find this resource and it is quite a lot more involved than the apt upgrade I feel was completely successful.