This got me zero good hits in the top 10: “ESXi 6.5” “vSphere Web Client” “VMware Tools” – Google Search
Since how to install/upgrade moved, here is a screenshot how to install or upgrade the VMware Tools using the “new” vSphere Web Client that standard in ESXi 6.5 and up:
It would be much more intuitive if the blue bar just linked to that action.
–jeroen