The Instant Access Points(IAPs) are different from the Instant-on APs. There is also a community dedicated to the Instant-on APs (here) Your question may be better suited for that forum.
That being said, I don't believe there is a way to manually upgrade the firmware on the Instant-On series without having internet access, as they download it from a cloud server. More information can be found here
(Full disclosure, I don't have personal experience with the AP-12, I just wanted to give you more paths to investigate)