Hi!
vShere client (C# client that you had to install on windows mahine) has been deprecated as of vsphere 6.5
Currently there are
VMware host client - this is a web client installed on ESXi host
VMware Web client (built on flash) - it's automatically installed on vcenter
VMware vsphere client (aks HTML5 client) - it's also automatically installed on vcenter
You don't need to install anything manually.
You can only upgrade host client separately.