"Update now" should redirect you to
/update?auth_token=thetoken. This was added 3.14.0 to provide more security to this process and avoid unintentional update. If your installation isn't redirecting to the auto_token version of /update, chances are that is because your files aren't actually updated (or delivered), which certainly is affecting javascript files but maybe it also PHP files are being cached in your server and the cache is delivering old stuff.
If you don't manage to get the working version, I suggest you co carry a manual update process as described in the documentation:
https://chevereto.com/docs/update-guide