You cannot delete your account, yet from the FAQ we learned the following:
To access, change or delete the personal information about your child on the Sites, log into the www.pokemon.com site and follow the instructions to unregister or contact us at The Pokemon Company International, Attention: Privacy Policy Administrator, 333 108th Avenue, NE, Suite 1900, Bellevue, WA 98004, Fax: +1 (425) 274-1041.
We’d suggest you check http://support.pokemon.com/ to file a ticket.
URLS:
http://pokemon.com