Typically, firmware updates related to the 2GIG GC3 are available either via OTA or via USB. However, currently, the 2GIG SP2 secondary panel firmware version of 1.2 is only available as an Over the Air (OTA) update via Alarm.com.
The SP2 would need to be connected prior to the firmware being pushed and the main panel should be on 3.1.2 or above.
The OTA process can take up to 12 hours to complete and if sent via cellular would incur a $10.00 data charge. If sent over broadband, there would be no charge.