Call the service department and give them the VIN and ask if there are any customer service campaigns or recalls for your car. There should be no charge for this. As freshcut says, some updates are only available based on a specific issue you may be having. Those won't be on the VIN-based list.When I asked my dealer about this, they said that the warranty would not cover for them to check the version of, or update, any firmware unless the car was displaying some kind of symptom related to that firmware. They don't just update every car, unless it is an update related to a recall program (like the one that turns the car off if left parked too long).
Does your heater heat well in electric mode? If not, you might need a firmware update...I have a 2013 Volt and I bought it used last month. I read that firmware updates improved the car even more, but how can I know if my Volt has the latest?