When you see a message to update your firmware, this means that Core needs to update its internal software to provide the best experience. This process happens automatically during initial setup and should only take less than a minute to download and install, depending on the speed of your internet connection.
Updates to your Core should happen automatically. Before a firmware update can begin, your Core will need to be at least 50% charged. If your battery level is too low to begin, the app will inform you that you need to charge your device. Place Core on its charging dock for 30 minutes, then try again.