Hi Craig, Any 'Firmware' updates are not downloaded to the SD card - they are designed to be installed into the operating system of your keyboard - probably via a USB link from a PC.
However, I would be VERY wary of installing any firmware updates, especially if the installation instructions are not clear.....
You could end up with a completely dead keyboard
I doubt if the 'upgrade' originated from the keyboard manufacturer, since Technics ceased production of keyboards early last year.
Why do you wish to apply the update ??
As has been said many times on this forum - "If it ain't broke - don't fix it!"