So domain names and WordPress.com blogs are separate, but you can link a domain name to your blog, so that when users go to your blog, they don't see the blog URL, they see a custom domain (like, twobeefy.com, or whatever else you choose). If you cancel your domain name that doesn't affect your underlying blog whatsoever - your upgrades are associated with your user account and the blog URL, not your custom domain.
So to answer your question - you can simply cancel the domain and register a new one - or map an existing one. If you give me a little more information about what you'd like to do next, I can help you with the steps.
Would you like to cancel your current domain twobeefy.com? I can help you do this, if you are not able to. Please understand that if you cancel it, there is no guarantee that you will ever be able to get that domain again.
If you have already bought a new domain but have not yet mapped it, you can use these instructions:
If you have not yet bought a new domain, you can do so through your site's Dashboard at Dashboard > Store > Domains.
I hope that helps!