Thanks, Tech!!
I admit that I am surprised by success in this case. It took a couple of hours to download the installer, and I did not want to get hung up in limbo, so I double clicked it to make sure it was good. It ran, without giving me a cancel option, do I let it uninstall the original program. I followed up with the uninstall utility and then ran the installer again.
At reboot, Windows reported inability to copy that file again, but it did not hang and did not repeat the attempt. Subsequent updates to the virus db have not required reboots and have gone smoothly.