Upgrades are applied on a workload domain basis. The management domain contains the core infrastructure, so you must upgrade the management domain before upgrading the other workload domains.
Take a backup of the SDDC Manager VM. The backup of this VM will contain backups of the other VMs as well.
Take a snapshot of each VM in your environment.
Do not run any domain operations while an update is in progress. Domain operations are creating a new VI domain, adding hosts to a cluster or adding a cluster to a workload domain, and removing clusters or hosts from a workload domain.
You must have downloaded the update bundles. See Download Bundles.