Took me a little while to figure this out but you need to make sure the drive you are using to transfer the firmware is formatted in FAT/FAT32, In my experience exFAT and NTFS don’t work. I have 5 PC’s in my house and all are running Windows 10. The only options I saw when formatting my thumb drives were exFAT and NTFS. All my drives were 16, 32, 64GB, None worked.
I then found a old 1 GB thumb drive received as a door gift at a conference. It was already formatted as FAT. I copied the 4 files and it worked perfectly.
If you have the issue where yo insert the drive and the New Firmware menu option doesn’t appear you may want to try another drive ir alternate format of the drive. Good Luck.