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When dealing with an update for your Garmin device, it is best to simply download, install, and use Garmin Express.
and (if you have a Windows PC) click on the big blue Download button at center bottom of the page. (If you have an Apple, click on the nearby Download for Mac link.) And download Garmin Express' installer to your computer, save it, then double-click upon it to install Garmin Express.
Then start the program, Garmin Express. Then connect your Garmin device. Then use Garmin Express to update your device.
If you have already used Garmin Express without favorable result, please tell me more about the case, using the Reply function... such as error messages when you try to access map update, etc. Also the age of the Garmin device, the model #, the source of the map update, the name of the file, and how you tried to apply the update, is important to the case.