If you are the owner of an organization, you can visit the organization's workspace in order to delete it. Select the organization in the workspaces area, and visit the "Settings" link in the sidebar. From there, if available, you'll see a section that will allow you to delete your organization.
You must enter your current password and then click on "Delete Organization" in order for the request to be submitted.
Your organization and its data will be deleted. If you have an active subscription on a paid plan, you must first cancel that subscription.