Add these lines to your wp-config.php
Note: Do not add this to the end of the file, but just below the database information on the top of the file.
define('FTP_USER', 'username'); // Your FTP username
define('FTP_PASS', 'password'); // Your FTP password
define('FTP_HOST', 'ftp.example.org:21'); // Your FTP URL:Your FTP port