You have two places to update this (well three, but we'll stick with the two).
If you can still log into your admin section, type the following for your URI /wp-admin/options.php - so for example, if your site is http://localhost then your full URL will be http://localhost/wp-admin/options.php. Once you've logged into your site you should see two Fields (well you'll see a lot of fields), but you'll want to look for the two with URL's in them - the Site URL and the Blog URL (in WP 2.7 the fields are labeled "home" and "siteurl", not sure on the other versions).
Or, you can log into MySQL database and run the following.
Select * from wp_options where option_id = 1 OR option_id = 39;
I just ran this today on one of my installs. If you're option_value is set to your localhost - you can then run the following:
update wp_options set option_value='http://www.yourblogname.com' where option_id = 1;
update wp_options set option_value='http://www.yourblogname.com' where option_id = 39;
This should update your table structure.