FAQ: Can I delete/replace maps from/in the GPS V's memory?

You cannot delete maps from the 19Mb memory of the GPS V. There is no need to do that, since it won't speed the V up and doesn't make room for more waypoints or tracklogs.

You can't replace single map chunks either. The GPS V and MapSource don't have that functionality. You can only replace the complete mapset from the V by uploading another mapset. Fortunately, since MapSource version 4.10 the uploading speed has increased. Uploading a full 19Mb mapset will typically take around 45 minutes or so.