To delete your organisation's Peakon account you must first have administrator access. Then, head to Administration > Company > Account > Data Control.
Below the other settings you'll see the option to delete your account – as is visible in the screenshot below:
Simply click the option to 'delete your account'. The account will instantly be blocked and no-one in your organisation will be able to access the account again. Within 31 days, all your organisation's data will be permanently deleted from Peakon.