Forza Horizon 2 not updating?
Solution 1:
Have you gone to 'My Games & Apps' then the 'Updates' tab within that? Any applicable updates to any of your applications should be in there. If you see an update for Forza Horizon 2, click on it and select download.
The other option is to uninstall and reinstall FH2. The reinstall should be downloaded with the latest patch.