Garmin have made a number of changes to their map update procedures in the last year.
For those with newer devices these changes have made it much simpler, for others it can still be a painful process with numerous calls to Garmin technical support.
In this case you update the maps on your sat-nav using Garmin Express which you download from Garmin's website and install on your PC or Mac.
You connect your sat-nav to your PC or Mac using the USB cable that came in the box.
If you have lost your USB cable you can get a replacement. Within Garmin Express, selecting 'Install All' under the 'Updates' tab is the safest option.
Download the Garmin Express app for free from the Garmin website, selecting either the Windows or Mac version.
The Windows version works on computers with Windows 7 and higher; the Mac version is for OS 10.10 and higher.
Even with several years of updating various models of Garmin sat-navs, I have found the experience torturous at times.