You can downgrade or cancel your Air account at any time. If you downgrade to the free plan you won't be charged anymore. If you choose to delete your company all data will be removed.
To downgrade to free plan:
Log into Air and click on your name in the top right of the screen
Select "Account Settings" from the dropdown menu
Hover over your company name and click the "Settings" button
Select the Free plan. Note: you may have to remove certain features to complete downgrade.
To delete your company:
To delete a company account you must be the company owner (the same person that created the company). Deleting your company removes all data and is irreversible.
Go to Company Settings from the top right menu.
Select Delete Company at the bottom of the page.