Firmware upgrades are automatically downloaded and installed when your speakers are connected to your home WiFi network. You do not need to undertake any actions for this.
For Citation devices with a display, you can go to System Info > Software Version to see which software version the device has and the date on which it was installed. For Citation devices without a display, you can see the software version in the Google Home app under Device Settings.
Would you like to know if a new software version is available? Then contact Citation Support for the most recent information.