GarminExpress will auto install the map in C:/ You would like to MOVE the map to a different location and have BaseCamp find it at that new location so that when BaseCamp is loaded and you go to the MAPS top line navigation and hit it you see your new map and can choose it. Here are the instructions
https://www.raidersporttouring.com/MoveGarminMap.htm
https://www.raidersporttouring.com/MoveGarminMap.htm