This page provides details on the uninstall process for V-Ray in Revit.
Uninstall
V-Ray installer will automatically uninstall any previous versions.
If you need to manually uninstall V-Ray, make sure that Revit or V-Ray components are not being used.
Then open the Windows Start Menu > Chaos Group > Uninstall V-Ray for Revit or alternatively run C:\Program Files\Chaos Group\V-Ray\V-Ray for Revit\uninstall\Uninstall.lnk .
This will start the V-Ray uninstaller. Follow the on-screen instructions to remove V-Ray from your system and restore any files overwritten by the installation.