To update your map you do it online with your Garmin connected to the computer. It's very simple. Just follow the instructions. The best value is the lifetime updates, especially if your device is rather new.
http://www.garmin.com/garmin/cms/sit...ppingsolutions
You also have the choice of buying an entirely new map. For example, if you were going to take it to America you would need to buy the whole map since your device would presumably and typically only have a European and region map on it. Those can be bought through Garmin and are available as micro SD/SD cards or DVD. You can even find good deals through E-Bay. Of course buying an entirely new map for another region or even your region will cost more than simply updating your existing map.
Call Garmin if you have any questions as they are well known for having fantastic customer service and will often give free updates to customers. Outstanding company and the best overall sat navs in the market.