Contact Elko support for the latest version of the thermostat firmware.
The version 1.2.6R package contained:
ap1.bin
avrboot.bin
elko_termo_og_boot.BAT
I bought a SanDisk 128GB SD card and formatted for FAT 32
using Disk Utility
(macOS). I unzipped the package and copied the files over to the SD card at the command-line. I am using the command-line to avoid any magic the GUI versions might introduce. I also rm'ed any hidden directories and files introduced by the OS. Unmount/eject the SD card.
The upgrade procedure is quite simple actually. As it states on the back of the thermostat:
Oppgradering:
1. Kurs av
2. Sett i kort
3. Kurs på
4. Oppdateres automatisk
5. Kurs av,ta ut kort
Cutting the power at the breaker, I put in the SD card, turned the breaker back on, and the screen will remain dark for approximately 10 seconds. Then the boot screen appears with the new firmware version. Cut the power again and remove the card.