The simplest trick is to download a new version of the software and the simply re-install it over your old installation. This way you will preserve the content downloaded, messages, custom settings, etc. However, if you have an antivirus application, add it to the exclusion list.
In most of the cases, a simple re-install fixes the problem without performing additional operations.
In case the above solution fails, completely remove the application, then use CCleaner to delete the faulty/obsolete registry entries and then perform the re-installation.