Default [Q] Updating HTC One M8 overseas

I have an HTC One m8 verizon but I'm currently using it overseas in a gsm/global area. Since the verizon software update section says that I can only update using cdma, I can't update the phone at all.

What are my options in order to update the firmware?

And if there is no way, what are my options to at least keep up with the newer android firmware? Sorry if this is a common question but I've just jumped onto android from an iphone 4s and everything is still alien to me.