If you are a Worldpac or SAVE or KW customer, the ftp location is: ftp1.sophiosoft.com
If you are an IMC customer, the ftp location is: ftpimc.sophiosoft.com
Sophio also requires you to use port 4421 regardless of where you site is hosted on our servers.
If you have problems you should double check to see that your 'passive transfer' button is turned on as well.
Lastly, make sure you are using an FTP client and not a browser to access ftp.