Hi,
There is no need for any special process and the installer should do that version upgrade uninstall the previous version automatically. When installing our plug-in(s), please double check you are not running any 3ds max related (like the VRay Spawner) service during the installation process. Sometimes, even closed, 3ds max might not shut down correctly and its processes are still running in the background. To check this you can go to the Task Manager by pressing Ctrl+Shift+Esc and make sure they've both have shut down correctly. That should help.
Best regards,