On a uIEC unit (any type).
dload the newest bin zip from www.sd2iec.de. At the time of this post, it is:
UNzip the contents onto the root of the first partition (on an SD card, you typically only have 1 partition, but for those uIEC/IDE or uIE/CF folks who read this...
Reboot the card (a reset should work, unless you have disabled RESET signal to the uIEC. Powering off and on will always work.
If the firmware is newer, the ACT led will start flashing. Once that is done, you are good to go.
If no flashing occurs, you are on the newest version, or the dload was corrupt (unlikely since it's in a ZIP file, which would not unzip if the file was corrupt, but just for completeness).
This advice *should* work for most sd2iec-based devices, but it depends on whether the manufacturer (or DIY builder) installed a "bootloader" on the AVR. If not (or if the bootloader code they installed expects some other way to update), then this approach will not work. A corollary to this: If the device does not have a bootloader and you cannot program AVR devices yourself (and even if you can), you might want to consider other options. Bootloaders are a *HUGE* timesaver.
0.10.3 has been out for quite a while, so I think you are at the newest version, but feel free to check. As noted, the error channel will show the version on boot.