Now that you know how to send a message with SwapNote, you might want to learn how to delete saved messages. Notes that you write and receive are saved on the Nintendo 3DS SD card. Yes, they take up blocks/memory. Deleting notes open room on the SD card for more SwapNote messages, 3DS apps, videos, music, and games.
How To Delete A Message/Letter in SwapNote
Important: Deleted notes can not be recovered to my knowledge. Attachments that were included with notes will also be deleted if the note was deleted.