Why can't I update my LG Tribute from 4.4.2 KitKat to 6.0.1 Marshmallow?

A

AC Question

I've been trying to update my LG Tribute to Marshmallow. I appear to be completely up to date on all of my updates except for my UICC Unlock update (which I have no idea what that is) which can't update for some reason. I keep reading that I should be able to update my device to Marshmallow, but I have a sneaking suspicion that either my device got left out of the update or I missed it somehow. If anyone has any ideas or knows anything that I'm missing, the input would be greatly appreciated. Thanks.

(The main reason I want to update is so that I can efficiently utilize my SD card by having apps directly install onto it. If people have any suggestions for that alternatively that would also be appreciated. - preferably without rooting my phone)