The only themes we can use on WordPress.com hosted blogs are licensed and adapted to run on our multiuser software the themes are found here http://wordpress.com/themes/ and in your dashboard at > Appearance > Themes
There is no FTP access to free hosted WordPress.com blogs for security reasons and we cannot:
upload any third party themes,
create child themes,
create our own themes,
create own own layouts,
or use stylesheets from other themes.