How to Delete your Nintendo Network ID!

WARNING! This process will delete all of your Nintendo eShop purchases, your NNID, and everything else on your system. I would only recommend this if you cannot access your NNID. If you know your password, you should be able to delete the NNID from the Nintendo Network ID settings in the System Settings. This process DOES NOT corrupt any game card data, nor your SD card data (just remove both when you format the system, just to be safe). Games that were pre-installed on the DS (downloaded before you got the system) should not be deleted, either. Miis aren't connected to the SD card, neither are downloaded games/content. If you forgot your pin number, go to System Settings, Parental Controls, then press "Forgot Pin" and answer the security questions to reset the pin.

If you remove the SD card before formatting, then the contents of the SD card will be saved (i.e. pictures).