Deleting unnecessary maps from your Garmin Nuvi will free up space for adding new maps. Always make sure that before you delete any map or file you are certain you will not need it in the future. Unless you are certain of the file's purpose, do not delete it. Be sure that the file you are deleting is the map you longer need or want.
Connect your Nuvi to your computer.
Open the Nuvi or the memory card drive, which ever contains the maps you want to delete.
Highlight the map you want to delete.
Hit delete on your keyboard.
Eject your device.