This article explains that the IP address and hostname of a vCenter Server do not change after an upgrade.
vCenter Server 8.0
The vCenter Server retains its original IP address and hostname (FQDN) after the upgrade process is complete.
During Stage 1 of the vCenter Server upgrade process, the installer prompts for an IP address for the newly deployed appliance. This IP address is temporary and used exclusively during the upgrade.
Refer to the following document for the vCenter Server upgrade procedure.