I don't have the N model
but I think you either update it with a DVD or USB drive. My family's GM vehicles are updated via DVD's. These prices are insanely high because of the contracts auto manufacturers have with these digital map suppliers.
As I used to participate in Tahoe/Escalade forums, I noticed this led many GM owners with navigation systems to download torrents, which are illegal copies of the DVD and burn them to disc therefore giving themselves a free update.
However, I also know that calling the suppliers help. I called ours and received a free disc update for our Escalade valued at $200. So trying that may help.
I want an 8.4N