To use plain FTP in filezilla please set up a new connection in Site Manager.
File > Site Manager
Select the New Site Button and name the connection.
Add the details of your ftp account on the right hand side.
Host - ftp.domain.tld or your server hostname.
Port - 21
Protocol - FTP
Encryption - Only use plain FTP
Logon Type - Ask for Password
User - Your FTP username
Password - Your Password
You can now test the connection by clicking connect.
