Fastvue TMG Reporter is subscription based software, and this entitles you to all upgrades and support free of charge (included in your subscription).
Therefore, you can upgrade TMG Reporter to a newer version and still use your existing license key. The software will still be registered as it was before the upgrade.
Before upgrading, you may like to backup TMG Reporter's Data Location first (location shown in Settings | Data Storage).
To upgrade, simply run the new installer over the top of your existing installation. The installer will pick up your existing settings, so just click next throughout the wizard without making any changes. Once installed, browse to the site and clear the browser cache by hitting ctrl + F5 (cmd + R on Mac).