To delete your user account on Outmind you just have to send an email to support@outmind.fr with the subject "Delete user account".
Then all the documents you were able to synchronize via Outmind will be deleted within 48 hours, as described in the article How do I delete my data ?
If you are an administrator of your organization for Outmind and you decide to delete all the user accounts of your organization, you just have to request the cancellation of your contract at support@outmind.fr with the subject "Contract cancellation".