Firstly you need to download VMware vSphere 6.5 ISO at VMware website, then restart vSphere 6.0 and boot up vSphere 6.0 by this ISO.
After it scans the VMFS partition, you can upgrade ESX VMFS datastore.
It starts to upgrade ESXi 6.5.
After it reboots the host.
After finished the host reboot, VMware ESXi 6.5 is successfully completed.