Before you upgrade the vCenter Server appliance, you must download the vCenter Server installer ISO file and mount it to a network virtual machine or physical server from which you want to perform the upgrade.
The computer from which you upgrade the appliance must run on a Windows, Linux, or Mac operating system that meets the operating system requirements. See System Requirements for the vCenter Server Installer.
Before upgrading a vCenter Server appliance, you must prepare the ESXi hosts in the inventory.
If the vCenter Server appliance uses an external Oracle database, you must determine the size of the existing database.
If vCenter Server appliance uses an external Update Manager instance, you must run the Migration Assistant on the computer running Update Manager.