Running vCentre as an appliance is becoming more common and with the latest version its very appealing over running as a Windows server. Updating the virtual appliance to a newer version of vCenter is easily done and the following will illustrate the process to upgrade vCenter appliance 6.0 Update 1 to 6.0 Update 2.
To upgrade vCenter 6.0 (without Update 1) there are some more steps, see VMware blog here.
You can download the latest .iso file or the upgrade .zip bundle from VMware or from the appliance you can update directly from the internet. First browse to the appliance using port 5480 and log in using root
Once logged in select Update down the left hand side. Select to update from URL and download the update. Once downloaded select Update – a reboot will be required
Once complete allow for a reboot and log back in, notice the new build number