the vCenter Binaries are available at following link.
https://my.vmware.com/web/vmware/details?productId=284&downloadGroup=VCL-VSP510-VC-510B-EN
Since its a remote upgrade, I woulld suggest using the approach in the followin blog if its just and upgrade of one or two host and internet access is available on host.
http://www.virtuallyghetto.com/2012/09/a-pretty-cool-method-of-upgrading-to.html