The upgrade of the appliance is a migration of the old version to the new version, which includes deploying a new appliance of version 6.5. You can deploy the new vCenter Server Appliance or Platform Services Controller appliance on an ESXi host 5.5 or later, or on a vCenter Server instance 5.5 or later. Your system must also meet specific software and hardware requirements.
When you use Fully Qualified Domain Names, verify that the client machine from which you are deploying the appliance and the network on which you are deploying the appliance use the same DNS server.
Before you deploy the new appliance, synchronize the clocks of the target server and all vCenter Server and Platform Services Controller instances on the vSphere network. Unsynchronized clocks might result in authentication problems and can cause the installation to fail or prevent the appliance services from starting. See Synchronizing Clocks on the vSphere Network.