Motorola has been one of the best Android manufacturer in updating their handset to latest iterations of Android, after updating most of its smartphones of 2015 series. Motorola has just started updating the Moto G 3rd Gen to Android 6.0 Marshmallow.
Android 6.0 comes with new handful features like Doze mode - which increases phone's battery life by closing all the background apps while phone's screen is off, Google Now on Tap, new app permissions and extended support of microSD cards by which you can combine your microSD card with internal storage to increase phone's storage.
The update is live in US and Canada for Unlocked devices first, more carriers and other countries will shortly get the update and the update size is 2GB.
Before starting the upgrade be sure to charge the device at least 50% and if possible connect it to a power source and get a faster Wi-Fi connection so the update will be downloaded shortly.