Hi again and thanks for coming back.
I believe you will use Garmin Express to not only install the maps on the SD card (while the card is installed in the device), but you can also use Garmin Express to update the device software - if needed.
Actually, I usually recommend that you make sure you have the latest version of the device software installed and working BEFORE attempting to install any maps (or updates).
Also, I did NOT see what size (capacity) of SD card you have installed, OR what type of computer you have, BUT can I assume that the computer CAN "see" the SD card - when installed in the device? NOTE: I believe the largest capacity SD card that can be used with this device is 16GB, but it could be lower (like 4 or 8GB).
Here is a link to where you can get Garmin Express for your computer. There is even a little video on that page that shows the basics of downloading, installing, and running Garmin Express.
NOTE: Please let me know IF and WHEN you have Garmin Express on your computer AND if the computer "sees" the device and SD card (when installed) BEFORE attempting to communicate with the device via Garmin Express.
This is important because of the registration request that often appears when you first connect your device through Garmin Express. If you have already registered the device, you will want to make sure you use the same registration information (such as email address) that was used when purchasing the maps that were downloaded.
Please let me know your progress.
Thanks, ***** *****