the normal procedure is this
1) Install mapsource and go to utilities, from the menu select “get unit ID”
2) Copy unit ID into JM keygen where it says enter unit ID
3) Select “custom mapset” from the map menu and put your map ID in, then press generate to get your key
4) Now open unlock wizard which can be found under “start/ programs” and follow the instructions
5) To check to see if your unit is unlocked go to utilities and select “manage map products”, then select unlock region tab, if you’ve done everything correct you will see your device next to the map you just unlocked
6) Now just transfer your maps to your device and your done

but i didnt tested this version i dont have Nuvi