Just follow the instructions in the Admin Guide in the section Upgrading from Gallery Server Pro 2.0 - 2.3. Even though the doc doesn't mention the latest version, the upgrade process is the same.
One potential gotcha: after you are all done with the upgrade open up galleryserverpro.config and make sure the setting silverlightFileTypes has these values: ".mp3,.wma,.wmv,.asf,.asx,.mp4,.m4a". That makes sure the Silverlight javascript files are sent to the browser whenever an album has one of these media types in it.
Roger Martin
Creator and Lead Developer of Gallery Server Pro