1) Login to your control panel(http://www.yourdomain.com/cpanel)
2) Click on "FTP Manager"
3) Click on "FTP Accounts"
4) Click on "Add Account"
5) Type in a desired FTP username next to "Login:"
6) Type in a desired FTP password next to "Password:"
7) Type in the name of the directory you want to grant the FTP user access to, next to "Directory:"
8) Click "Create"
NOTE: Make sure to yourdomain.com with your domain name.