If you have a web server it is not necessary to have a FTP server but have users SFTP. The problem next arises is to restrict users to their respective www directories and below are the steps to restrict users.
#Create a group for SFTP
$groupadd sftpwww
#Create a user
$useradd john9
#Add user to group
$usermod steve -g sftpwww
#If you want to deny the user to any ssh access then
$usermod john9 -s /bin/false
#Set users home directory and in the case assuming its a www folder
$usermod john9 /var/www/html/www1/public_html
#Restart SSH
$service ssh restart
#And add at the end of the /etc/ssh/sshd_config
#Restricting sftpwww group users to their home directory
Match Group sftpwww
ChrootDirectory %h
ForceCommand internal-sftp
AllowTcpForwarding no
Match user john9
ChrootDirectory %h
ForceCommand internal-sftp
