Autoupdate in version 2.0 an higher will check for newer versions if it has not successfully checked within the past 7 days. This check should be completely seemless and you will recieve no notification if no update is found.
On Windows Vista and Windows 7, MegaLogViewer does not by default have the required permission to replace the files under Program Files. This will cause an update failed message. You must use "Run as Administrator" to provide the needed permissions. On Windows 7 this can be accomplished by right clicking on the the icon your use to start the application and select "Run As Administrator". Then by using "Check for updates" under the Help Menu, you will be able to complete the update.