When I had Zumo 660s on my Spyders: I had to plug them into my computer, and link up with Garmin's website.
Can you look up your model online, and read the instructions?
(My bikes were 2010, and 2014 models.)
A lot of them are done by downloading the update to an SD Card and then plugging the SD card into the back of the radio to complete the update. Yes sometimes it means removing the radio to plug in the card.