Can't Upgrade My Moto G 3rd Gen to Marshamallow??

[AC Question]

I just got a Moto G (2015 model) and it doesn't seem like I am able to upgrade to marshmallow because it's Virgin Mobile. Whenever I go into software update it simply says "no new updates available" and yet the phone is still running Lollipop...Is there anything I can do (root the phone, possibly install a custom rom) that's relatively safe which will let me download it?? I figured this would all be taken care of since Motorola released the update in January!