The 1.8 firmware is ONLY for the original Kobo. It is actually version 1.8.1. You should be offered the firmware when you next use the desktop application. If not, you can force an update by pressing Control-shift-u (Command-shift-u on a MAC). Please make sure to read the
first post on installation thread first. Doing a factory reset BEFORE you update is strongly recommended, as is deleting any of the books sideloaded through Calibre or drag and drop.