There is no FTP access to free hosted WordPress.COM blogs and we cannot install individual plugins or any themes into them The themes found on the internet are for wordpress.ORG installs which run on different software.
On free hosted wordpress.COM blogs we can only use the themes which have been coded to run on this multi-user software and made available to us here. > Appearance > Themes and no others. We cannot edit either themes or templates on free hosted wordpress.COM blogs. > http://en.support.wordpress.com/themes/editing-themes/
If you wish to have complete control over a blog, the ability to upload themes and plugins, and to edit themes and templates then your option is to hire a web host and get a free software install from WordPress.ORG and self host it.
Please read > http://en.support.wordpress.com/com-vs-org/
If you are moving the content from the free hosted WordPress.com blog into a WordPress.org install. You create an export file and place it on your desktop. Then you import that files into your WordPress.org install. The content you can move by export and import is posts, pages, comments, custom fields, categories, and tags and links. All content in text widgets must be copied and pasted. No WordPress.com free themes or premium themes can be exported and used on WordPress.org installs as the two run on different software.