Windows : press button. Wait interminable time whilst it downloads and Does Stuff. Works.

OpenBSD :
sysupgrade. Literally *just* sysupgrade most of the time. Go for cup of tea, come back, done.

syspatch. reboot if necessary and there are patches.

pkg_add -u. Done.

FreeBSD :

freebsd-update fetch
freebsd-update install. Wait some time.
reboot
freebsd-update -r <release number> upgrade
freebsd-update install. Wait absolutely fecking ages.
reboot
freebsd-update install

pkg upgrade
(plus manually fiddling around removing the drm kmods and re-adding them)