Updating ESXI - mrblumbo/ESXI GitHub Wiki
If you're running the free version of esxi and you want to update the build version, you can use this link.
http://download3.vmware.com/software/vmw-tools/esxui/esxui-signed-latest.vib
It should install the latest signed venison of esxi onto your system. A reboot should do the trick to update the build number.