This guide contains instructions on how to delete an account. If you wish to archive an old account instead, please see this article.
There are three ways of deleting an account:
swipe left on the account to reveal "Delete" button,
enter account edit mode by clicking the edit button at the bottom of the accounts list, click on the red (-) button to the left of the account you wish to delete and then on "Delete" button that appears on the right,
or bring up the contextual menu and select "Delete".
You'll be warned that the action is irreversible. Furthermore, when you delete an account, it deletes all transactions and if transfer transactions are among those to be deleted, they'd be deleted from both accounts, causing other account balances to be affected as well. However, you can tell MoneyWiz to convert transfer transactions to expenses/incomes (depending on the amount). If you do this, you might want to run a category report to find uncategorized transactions and decide how to categorize converted transfers.