The upgrade of AOS in a Nutanix cluster can be performed via Prism using a 1-Click approach. Upgrades are non-disruptive in the sense that when a VSC is taken offline to be upgraded, availability is still provided by the other VSCs. Nutanix provides a step-by-step upgrade guide that includes a number of pre- and post checks.
AOS 5.17 introduces support for upgrading AHV hosts through the Nutanix Life Cycle Manager (LCM).