This applies to the eShop on your mobile device. Follow the steps named in the link.
URLS:
http://www.nintendo.com/3ds/downloads
http://www.nintendo.com/consumer/systems/3ds/en_la/ht_apps.jsp?menu=nintendo%20eshop&submenu=ctr-ht-apps-eshop-remove-account
If you face any technical problem you can call on toll free number
customer helpline phone number is +1 866 940 OOO5