I'm in the same boat, and I've been unable to find a solution. Fairly sure that it is an OTA update only, and MS says it's controlled by the carrier.
Annoyingly/Interestingly, Samsung lists the Kies software on the support page for this phone, and that software has the ability to download and flash firmware...but Kies is, by everything I've read, only for Android devices. Why it remains on the Samsung support page for this device is beyond me.
Of course, I went ahead and tried it, couldn't connect to the phone as expected. Asked Samsung about it and then told me to send the phone in for repair without addressing the software question.