If a client no longer wishes to be under the partner account you can transfer ownership of that company back to a client user. The user involved must be an existing user on the company, you can add a user to the company for the purpose of transferring ownership.
To transfer ownership:
1. Select the 'Number of users' option on your dashboard followed by 'Manage users'
2. Eligible users will have a 'Transfer Ownership' option shown against them, choose the relevant user and hit that option. This will immediately transfer ownership to the client and remove the company from the partner account billing cycle.
If you need to remove yourself from the company too you can do so using the 'Leave company' option that will now show against your user.