I can't be sure about your unit but what usually works with Kenwoods is to connect it to your pc via rear (mini ?) usb slot so you can see it as an external storage device. This way you can access Garmin files but what you need to do first is to install Garmin's USB Drivers

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Before you do anything make a full backup of Kenwood's internal memory including hidden and operating system protected files, better safe than sorry. You can change the settings in Windows to make those files visible under Folders menu.