Is the device is successfully syncing to the Kobo server? And what affiliate is is in the ".kobo/affilate.conf" file? Some, such as Rakutan, don't allow all the firmware versions. Changing this to Kobo, will usually fix this.
And to do a manual upgrade, see
https://www.mobileread.com/forums/sho...d.php?t=185660. That has links to the firmware and instructions in the first few posts.