Okay i found the hidden system folder already! I forget you also should put the settings ; show protected system files.
Now i can see the .system folder.

I succesfully updated my Nuvi 3790, first time it show me river and green while driving around!
And even warn for red light camera now! Wow!

Catymag do an good effort for explaining everything.
I wish i now my nuvi same like you!

It was a little puzzling the first time, but my nuvi works perfekt and is as new.
With an sd-card and this handy gps forum, i read and found out everything already.

My wife very happy with her updated 3790 and me with my 1490!