Backing up through wordpress.com and moving to godaddy hosting

I created a wordpress.com account, and recently purchased a domain and wordpress hosting from Godaddy.com. However, I’m having some trouble backing up my current DB from wordpress.com….

I’m pretty sure that once the back up is done, I will be able to restore the files onto the mySQL db through godaddy, and edit what I need to in the wp-admin.php file….. But first step is backing up. How do I do it from within the wordpress.com online interface?

Can anyone help me?

Any help would be appreciated 🙂
Thanks a lot!