If your vCenter has no Internet access, use the following procedure to upgrade it:
Go to https://my.vmware.com/en/group/vmware/patch#search
Download the
VMware-vCenter-Server-Appliance-6.0.0.30000-5112509-patch-FP.iso
Copy the .iso to the ESX datastore
Connect the .iso file as CD ROM to the vCenter VM
Login to the vCenter Appliance via Web Browser
https://vcenter:5480/index.html#/update?locale=en
Choose "Check updates" > "Check CD ROM"
Then choose "Install updates"
Once the update is completed, click on "Reboot" on the summary page