Go to https://www.cisco.com/c/en/us/support/servers-unified-computing/ucs-c-series-rack-servers/products-user-guide-list.html and select the correct HUU guide for your system/firmware.
Check your compatibility matrix here for hardware/firmware/OS to be installed
https://ucshcltool.cloudapps.cisco.com/public/#
https://kb.vmware.com/s/article/70785
https://www.vmware.com/resources/compatibility/search.php
https://interopmatrix.vmware.com/Upgrade
https://kb.vmware.com/s/article/78205
Check your VIB drivers on your ESXi host to see if they need to be updated as well. https://kb.vmware.com/s/article/1027206
You will be looking specifically for the nenic and nfnic drivers for any CISCO VIC cards, and potentially any other brand of network adapter that my be in a PCIe slot. You will need to download those VIB drivers from the vmware.com Customer Connect center under downloads for your vSphere version. These will be used later on, after the firmware upgrade if applicable.
https://customerconnect.vmware.com/downloads/info/slug/datacenter_cloud_infrastructure/vmware_vsphere/6_7#drivers_tools
This will be a disruptive process, so the VMs have to either be migrated off to another host in the cluster, or shut down if they are not able to migrate off the host, as the UCS C-Series CIMC KVM has to be used to boot into the HUU ISO.
You will update all applicable firmware on the server. The server will reboot, and you will lose connectivity. After 5-10 minutes it will be reachable, you will need to refresh and re-accept the default certificate if this hasn't been changed once it comes back online.
After the firmware upgrade, if you were also upgrading your vSphere ESXi version you would want to do that in the correct sequence, depending on your environment. Once ESXi is at the correct level, either upgraded or left alone, then verify the VIBs, and if updates are required run and are the correct version.
https://kb.vmware.com/s/article/2008939
