index points to the wrong address

Hello. I’m having some trouble with a wordpress blog I have installed. This morning I was trying to install a link on the top of the blog page that would point to my professional website.
I clicked on the settings tab in the admin page. While there I thought I would change one of the addresses to michelleheaps.com instead of blog.michelleheaps.com.
After doing this I tried to click on another tab in the admin but it kept coming up with a 404 error saying michelleheaps.com/wp-admin/index.php does not exist. I know it won’t work because it’s pointing to the wrong address. It should be blog.michelleheaps.com/…..
So I tried typing it in manually (blog.michelleheaps.com/wp-admin/index.php/) Still won’t work.
I looked in the wp-config.php file but I can’t find anything that makes it point to the right address.
I’m stuck and would appreciate any input. Thanks.