Hmm? So it says it can update it, but then doesn't? I'm stuck.
Can you send a screenshot to email@example.com and I will look into it, please?
Unfortunately, it may be that you will need to uninstall through the app and then reinstall it.
I know there were problems on one of my other games where the app would not let people have both the demo and the game installed at the same time.
I am not sure if uninstalling it will affect your saves - I am unsure in the case of the app where they are held, otherwise you could just copy the folder and then put them back into the new install.
Sorry this has become an issue for you.