When attempting to upgrade LMI 6.2.0 to any future supported version the upgrade can fail very early in the process before the first reboot occurs. The error indicating the upgrade failed is displayed in the File Update page but nothing is displayed regarding the cause. One of the symptoms is that the text field that shows the various stages of the upgrade will not display any progress text, such as when the authenticity of the upgrade file is being verified. If you don't see any of this output in the text field then it's an indicator the upgrade will fail. It may take 10-15 minutes before the upgrade process actually fails.
In contrast, when the upgrade process is functioning correctly you should instead see a status like that shown in the following screenshot: