How can I update the OS on my ZTE?

[AC Question]

I am on my second ZTE 936L and am trying to upgrade the OS on it from 4.4.4 to 5.0 or above. I know it can do it because on my first one, I was able to do it. I have already contacted the manufacturer and the service provider and both told me I would have to contact Android. How can I get this done?

 

[B. Diddy]

Welcome to Android Central! Are both of these phones obtained directly from a carrier? If so, which one? Was the Lollipop update for the first phone pushed over-the-air, or did you manually install it? Are you still on the same carrier, or did you take the second phone to a different carrier?