http://download.kobobooks.com/firmwa...ade-1.9.10.zip
Back up your books. Do a factory reset to your Kobo. (There is a button to do so in the Device Information configuration screen.)
When the kobo is done restoring itself, extracts the contents of the zip file into the .kobo directory. Eject/Unmount the Kobo as usual and the update to 1.9.10 will be done immediately after.