OR If you can still ADB into the your FTV then just follow the "Update Process" instructions available in the FiredTV GitHub.
To update to a newer version of this app, first you must uninstall the old version.
You can do this on the FireTV itself (Settings > Applications > Manage Installed Applications > FireTV Launcher > Uninstall)
Or, you can use adb:
adb connect xxx.xxx.xxx.xxx to connect to your FireTV where xxx.xxx.xxx.xxx is the IP address of your FireTV adb uninstall com.altusapps.firedtvlauncher