> Do I need to install FTP than install SFTP over the top?
Not necessary. Just install SSHD (if not installed already). SFTP is a SSHD subsystem and is operated by a helper which location is configurable in sshd_config (/usr/libexec/sftp-server, or /usr/lib/openssh/sftp-server, or /usr/libexec/openssh/sftp-server in different flavors of Linux). SSHD also provides SCP mechanism (which does the same thing – file transfer over encrypted channel). Be aware that SFTP doesn’t use TCP ports 21/20, both it and SCP use TCP 22.