You must make sure your account privileges do not exceed any of the Basic package limitations and then fill out our cancellation form accessible through Administration => Account > Account Status. Specify in the “Reason for cancellation” field that you wish to continue using the free account. Your account identifiers (Account Name and Subdomain) are indicated under Administration => Account > Edit Account.
Warning: Free accounts are automatically deleted if 30 consecutive days go by without a single login. We strongly suggest you set up a reminder for yourself to login at regular intervals in order to avoid having your free account auto deleted.