I assume you are using the default VMware ESXi image (i.e. no OEM build) and DRS is not available!?
I further assume that vCenter Server as well as Update Manger are already up-to-date.
- Import ESXi Image
- Create "Host Upgrade" Baseline using the imported image
- Attach the Host Upgrade Baseline to host or cluster
- Attach the default Patch Baseline (or an individually created patch baseline) to host or cluster
- Enter Maintenance Mode (this will only start the task, and finish once step 6 is done)
- Migrate VM's off the host
- Reboot the Host (may not be required, but good practice)
- Remediate the Host
- Check Host settings (e.g. networking, storage, date/time...)
- Rescan the host twice for updates/patches
- Remediate the patches if applicable
- Check Host settings (e.g. networking, storage, date/time...)
- Exit from Maintenance Mode
- Migrate VMs back to this ESXi host
I usually use the maintenance window to upgrade the host's firmware too (e.g. between steps 7 and 8)
André