Hi,
I have done such functionality before.
Usually after every start, application checks against a web link for a release note, and if newer available, downloads it and refreshes itself. This pattern can be tuned for your needs of course.
There could be funny cases when the application runs on a PC with access to the internet through a proxy.
If you will share more detailed information about the application, and the update mechanism you wish to apply, I can give you a more precise date estimate. It should not take more than couple of days.
Regards, Attila