RAK gateways don't have remote management capabilities. But, it's pretty easy to upgrade the firmware yourself.
  1. Find the IP address of that gateway on your network. You can log into your router to see the assigned IP address to RAK
  2. Unzip this file
  3. Log into RAK gateway at the IP address. The default credentials are: username: root, password: root. It will first come up with a security screen "Your connection is not private". Click "Advanced" and "proceed"
  4. In the left pane, click System->Backup/Flash Firmware, then "Choose File" - the one you unzipped earlier, and press "Flash Image..."
  5. That's it.