The unit will erase existing maps on the unit when you load new maps on it.
The “fix” is easy. Connect the gps to your computer and download the existing Map Set, if you have not saved this Map Set, do so now. Having done that use the Map Tool in the Tool Bar and select the maps that you want to add to the Map Set. Now your software will show 28+ maps. Save this Map Set on top of the old one in your computer or create a new file for it. Then install the New Map set.
At this point you have room for approximately 230 more maps. (+or-) In my case I loaded the Topo Maps for some of the cities I know my wife has relatives. (It is always good to have an excape route.) You can use Yahoo or MapQuest to get a street address. I used Microsoft Streets and Trips, and created a waypoint based on that information. I was pleased that it put me within 100 feet of the correct address.
