We all know how important it is to make sure old urls are redirected to the new ones so that it does not affect search engine ranking. Luckily, if you are using pathauto and redirect module, it is very easy to do so.
Here is how to do it
1. Go to http://example.com/admin/config/search/path/settings. Select option "Create a new alias. Leave the existing alias functioning"
2. Go to http://example.com/admin/config/search/redirect/settings and make sure "Automatically create redirects when URL aliases are changed." checkbox is ticked.
3. Go to http://example.com/admin/content, select nodes and choose "Update URL alias" from Update options dropdown and submit the form.
4.Confirm the redirects at http://example.com/admin/config/search/redirect
5. You are done!