You may change your mind about the patterns you've set up using Automatic Nodetitles, or you may realize that you created a number of nodes before you set up your Automatic Nodetitles patterns for URL paths. In either case, you'll want to update the URL paths to reflect the new pattern. (Note: if your site has already gone live and people may have linked to a page using its current URL, you may want to install and configure the Redirect module to automatically redirect the old URLs to the new one.)

Once you have changed the Automatic Nodetitles path configurations to your liking (at Configuration > Search and metadata > URL aliases > Patterns) you can use the Views module (see chapters 12 and 13 for more on Views) plus the Views Bulk Operations (VBO) module to update the old paths.

See "Adding terms in bulk with Views Bulk Operations" for instructions on basic view configuration using VBO. For this view, under "Selected bulk operations", check the checkbox for "Update node alias" instead of "Modify entity values". Proceed with the remaining steps as described in "Adding terms in bulk with Views Bulk Operations" (i.e. go to the page you created with Views, select the nodes, select the "Update node alias" operation, and execute.) This will change all the existing paths to match the new pattern.