Thanks, Larry. I've tried these steps many times with no success.
Let me trace the path I've been taking and see if you can spot where I'm going wrong.
I followed your pointer to GenHu site
Read through his instructions titled Upgrade NanoVNA use DFU.pdf
Clicked on my desired .dfu, and download the file NanoVNA-H_AA_20191009.dfu, which I stored in the same folder as DfuSeDemo.exe.
Connected NanoVNA to Windows 10 USB port and started up NanoVNA in programming mode.
This generates a new directory named Universal Serial Bus devices, and it contains a driver named STM32 BOOTLOADER
I've seen screen shots of successful firmware updates, and they show this new file to be in the Universal Serial Bus controllers directory, and the driver is named STM Device in DFU Mode.
If I could get past this driver problem then I think the rest would fall into place.
