Deleting your Trello account
You can easily delete your Trello account by visiting https://trello.com/your/account and clicking the "Delete this account?" link at the bottom of the page. Trello will send you an email which will ask you to reconfirm the deletion of the account. Once you confirm that, your account will be deleted.
Admins of Boards and Teams
If you are the sole administrator of a board or team with multiple members, before you can delete your account, you will be prompted to choose a new admin for those boards and teams before your account can be permanently deleted.
Deleting an account does not cancel Business Class
If you are the only member of the Business Class team, then your subscription will be cancelled when you delete your account. Gold subscriptions will also be cancelled if the account they're associated with is deleted.
However, if you're the admin for a Trello Business Class team with multiple members, deleting your account will not cancel your Business Class subscription. Instead, you will be prompted to choose a new admin for that team before deleting your account, and the subscription will continue. At that point, only the new admin will be able to cancel the subscription.
To cancel your Business Class subscription, see: Cancel Trello Business Class.