StreetPilot C330/C340 map updates

There is no staright access to its memory, thus, trying to install a map with the mapsource or else produces "No available memory" response. At least the one need to access the memory & delete the old map. Any help/URL?
Thank You

You can use actual maps on SD card up to 2GB. The preinstalled internal map you should deactivate in menu.