Only the account owner can cancel an Open Leads account. If you are the account owner, log into your Open Leads account, and then click on "Settings" and then on "Billing."
Click on the "Cancel Account" link, and you will be given the option to export your Open Leads data, and to confirm the cancellation.
Once successfully canceled, you will receive confirmation via email, and your account will be deleted at the end of the current billing cycle.