Repost of http://www.elektron-users.com/index.php?option=com_fireboard&Itemid=28&func=view&catid=9&id=120877. This actually works! I upgraded my MDUW to 1.63 last weekend. In case elektron-users.com is ever taken down, I want to make sure this information is preserved.
To list available midi ports with alsa midi CLI tool:
$ amidi -l
To upgrade firmware:
$ amidi --port=hw:1 --send=Elektron_SPS-1UW_OS1.63.syx
where port is the alsa device name from the first command.