The current firmware version of a device can be seen by clicking View > Device Status from the menu, or visiting http://DEVNAME.egaug.es/status.html (replace DEVNAME with the device name of your eGauge). The current firmware version will be listed next to Firmware:
Sample Status Page
The small blue link next to the firmware version will open the firmware release notes page, where changes to the device firmware are tracked. We recommend updating the firmware on a regular basis.