If you're planning on upgrading soon, you might want to wait until then to start really mucking around -- this problem may have already been fixed. (And don't forget to back up your database and files before upgrading, of course.
That said, a couple of things you can check out or try:
1. Make sure that the footer wasn't hard-coded. You can take a look at the footer template file to see if that copyright information was added by hand. See templates/common/footer.tpl.
2. Check the database to see if the footer information is in there. If you have access to phpMyAdmin or from the server, take a look at the journal_settings table. There should be a journalPageFooter column in there, with your footer text included (only if the footer text was added via the UI, and not hardcoded as above). You can update that field with the appropriate text via MySQL, and it should work fine.
Let us know how it goes!