Plugin for redirecting to new folder?

I had my blog at a sub domain but have now installed it on the root domain and imported all my posts and pages to the new install.

How do I get all references to my old sub domain in links now show for the new domain? Is there a plugin for doing that or a code or something please?

Example: I want any references to http://family.thomases.org to now show as http://www.thomases.org for all posts that might link to other posts.