When do I need to update my GPS maps?

I am a traveler and using GPS technology for finding the unknown locations or places. I am using this technology from the last three months, so I cannot say that I have complete knowledge about Garmin GPS technology. I know that I should update my Garmin GPS unit on a regular basis. I don’t know when I need to update my Garmin GPS unit. Due to insufficient knowledge, I am not able to update Garmin GPS unit. Really, it is a very difficult job for me for Garmin updates. Therefore anyone can recommend the best ways to update my Garmin GPS maps.