changing page url name

I posted this in the How to forum and it was not answered satisfactorily.

I want to change the url of my page:

https://www.insuranceclaimhelp.org/free-policy-copies/

to:

https://www.insuranceclaimhelp.org/policy-form-copies/

When I use edit Permalink on the Manage Pages control panel and select save, the page fails to load on the website.

Is there some other file that I have to get into on the server that can’t be edited by WordPress?