Many Thesis theme users have had this small gripe – they haven’t found an elegant way of removing the attribution link from the footer which they are allowed to if they have the developer’s edition of the Thesis theme for WordPress. Welcome to the world of hooks. As a result of well thought and intelligent coding, Thesis relies on the WordPress hook system and comes with its own numerous hooks. While it will be pretty straightforward to add html with the hooks, removing it may be the hidden side of the coin. Here’s a simple oneliner that you can use in your custom_functions.php file to remove the attribution link.
As such you can also remove other html in a similar way. See the entire hook reference at the Thesis theme’s blog.
WordPress Support & Maintenance, Thesis WordPress Theme Framework