If you use the Joomla forum extension Kunena, here's an easy way to remove the obnoxious footer backlink.

There will be cases where you need to set up a permanent redirect from an old path to a new path. It also allows search engines to know they need to update the links. I would recommend using redirects via your htaccess file rather than using the redirect manager in Joomla! unless it's only temporary.

So you procrastinated too long and didn't renew your domain name or there's a specific name you want that's already in use...