I'm just wondering if someone can tell me how to stop an ftp user from being able to go back dirs.

Right now I have the ftp account setup and working, and it starts in /var/www/html/site. The reason for this is of course to allow ftp access to edit the website. My problem is, that right now once they login they can go back as far as root (/). I don't think they can actually edit anything, but I would like to make it so they can't go any furthur back then /var/www/html/site.