To update any GPS device, connect it to a computer using a USB connection or the SD card that came with your GPS device. You will be prompted on the computer screen after the GPS is linked.
After connecting the GPS to the computer, the computer will verify the version of the software and map data on the computer, and you should be able to see the choice to download the maps.
The maps will be downloaded and transmitted to your GPS device once you click the Download Maps Button (the name of the button may change depending on the manufacturer).