The display has its own controller with an own firmware. You don’t update it separately (there is no separate UI firmware available), but it will get updated automatically when you update the rest.
In very few occasions the update of the UI firmware can silently fail. If this is really the case, then try to re-apply the 1.30a update. If it still doesn’t change (and you are really sure it should be v1.8), contact Elektron support.