I normally update via the Updater tool, but when that fails I generate a backup using the web interface, and then re-flash the flash drive with the latest image.
Sometimes restoring from the backup doesn't work, but if you just look in the backup tar all it is is a copy of a bunch of files. It is easy enough to put the kstars files back where they should be as everything is relative to the root / directory.
The only annoying part of this is I have to connect to the hotspot and re-input my wifi password, but that takes all of a minute.