Important: The subdomain must be created before you can create an FTP user for it.
From the dashboard, choose a plan. Click the files tab and click FTP. Click create a new FTP user. In the username field, enter the subdomain name without .yourdomain.com (for instance, enter “news” as the username for the subdomain news.yourdomain.com). Enter a password and select the type of account you want to create, then click save FTP user.