Please post the complete clickable URL for the blog in question starting with http://
Then please read this entry expressing the differences between free blogs from and being free hosted by wordpress.COM and software installs for self hosting form wordpress.ORG. http://support.wordpress.com/com-vs-org/
There is no FTP access to free blogs from and being free hosted by wordpress.COM and no individual plugins can be installed in them. Plugins are only used on wordpress.ORG installs.
Once you post the URL for the blog in question we will be able to provide applicable answers and advice.