There is a pathconfig.php file in the root directory of each weblog. The purpose of this file is simply to the path and URL to the LnBlog installation and to define the URL to the blog root directory. You can edit these values with the blogpaths.php page.
Note that the only time you would really want to change this is when you move your LnBlog installation folder, either as part of site cleanup or because you are changing web hosts. In either case, another easy method is to simply delete the pathconfig.php file for your blog and run an upgrade on the blog from the administration page, which will recreate it.