Uninstall, smartly remove remaining files from file directory, go to Nvidia's website and download the latest (if available) version of the driver, restart PC, let windows auto-install an older version, install the one you downloaded, restart and it should all be fine.
Because it is going to anyway, if he tries to cancel it in between it is very likely he can mess up the installation and may cause damage to the upgrade from then on. Where as there is no harm as Nvidia's latest driver will get rid of the older one anyway and it should all be fine.
Actually more than an upgrade it should always be a clean install with the new drivers.
As for new drivers getting rid of the old ones, well, it does not always occur (if at all) as it is a common source of driver/graphic card problems.
Also, using WU for this kind of matter....for patches for their own OS I kind of understand it but "fiddeling" with hardware drivers when they may not even be the most up to date ones (leaving aside a proper discussion on if the most up to date ones are always the best option).
Maybe disabling the WU service would make it easier to do the things the way they should be done?