Thanks, Alessandro, but that looks like the admin had a Windows vcenter server. I have the linux based vCenter server appliance, so only update manager is running on Windows.
You can un-register the Update Manager extension from vCenter and you will be upgrade the VCSA 6.0 to 6.5 or 6.7 which has embedded Update Manager available.
Follow the steps below to remove VUM extension.
In a web browser, navigate to http://vCenter_Server_name_or_IP/mob
Where vCenter_Server_name_or_IP/mob is the name of your vCenter Server or its IP address.
Click UnregisterExtension. A new window appears.
Paste com.vmware.vcIntegrity and click Invoke Method. This removes the plug-in and results in void.
Close the window.
Once done, go ahead and upgrade the existing VCSA.
Do let me know if you have any further queries.
Thanks, Nirmal. That appears to have done the trick.