Updated maps for 2015 Prius Four?

I am seeing conflicting information on line about update maps for the 2015 Prius Four's navigation system. E.g.,
(a) whether all one needs is the (micro?)SD card with the map, or
whether one needs some activation code from the dealer, or whether even only the dealer can do the update;
(b) whether there even *is* an SD card containing the map, or whether the map is stored internally and is upgraded by attaching a thumb drive containing the map;
(c) if there *is* an SD card, whether it is hidden under a cover in the nav. system surround (I certainly don't see a removable cover there), or whether it's in the console under the armrest (I don't see one there either -- only a USB port and the (cigarette lighter)/power socket).
I cannot find this information in the manuals that came with the car -- nothing there about map updates at all.
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