Den in USA

it should be in extras, you should be able to update it. Or otherwise you can try uninstalling your current app and the installing it again from extras. In app manager try pressing the "Check for updates".

Anyway, here is the link to downloads page:
http://maemo.org/downloads/product/OS2008/theremin/

And here is the direct link to install file (click from tablet browser to install):
http://maemo.org/downloads/product/r...et_installfile