Patch your Mapsource ,instructions and file here
[Only registered and activated users can see links. ]
send the selected map to your pc: you'll have a gmapsupp.img , drag and drop it in the icon of this soft
[Only registered and activated users can see links. ]
your map will be unlocked, copy it in your sd in a Garmin directory

or alternatively
read and follow this thread
[Only registered and activated users can see links. ]