The BigCommerce eCommerce software does not support the use of FTP. As of August 31st, 2013 BigCommerce has stopped supporting the ftp function and encourages business owners to switch to WebDav
WebDav is similar to FTP, however is a more secure protocol and hence BigCommerce has decided to make the switch.
You can refer to our articles on ‘How to use WebDav in BigCommerce’ for further reference