Hi my name is ***** ***** I will be the expert working with you today to help resolve your problem.
To update your map with the latest update you will need atleast a 4GB sd memory card which must be formatted and inserted in an card reader connected to your computer with internet.
Or you can use your usb card that can connect your gps to the computer you will need winzip program which can be downloaded free from the internet and your garmin gps
download winzip from this link: http://updatedigitally.weebly.com/
refer this video link and let me know if you find any problem in updating the garmin
The model Garmin DNX42308T is not listed Garmin/Kenwood website, does it matter which model I pick to down load the maps?