First login to your account from Client Area and choose the "My Services" link. Then click on the “Product Details” button to see the details of the product or service in question.
On the “Product Details” screen you want to scroll down the window and select the “FTP Accounts” button.
In the “FTP Accounts Management” screen you will be able to add the name of the new FTP account, password to the new FTP account, and directory for the FTP account. You will also be able to select the quota size of the FTP account. Once you have done this just hit the “Create” button.