This tutorial will teach you how to change which map you are viewing on your Garmin GPS unit. (http://www.gpsfiledepot.com/tutorials/how-to-change-which-map-is-displayed-on-a-garmin-gps/)
Updated; figured this tutorial was long overdue. next up: FAQ...
If you have questions or problems with this tutorial, please start a new thread to discuss your situation and give details such as the gps model, map (with a link to the map) etc.