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What exactly does the error message about 'permission' say?
And, are you accessing with Garmin Express? if not, it would be right to try it using the Garmin Express program on your computer:
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.