What if you NEED to change the media URL if it has changed, for example if you must change your site URL or need to update the location of your file uploads (say to something other than "/wp-content/uploads/")? Or say, if you upgrade your WP site in a different "home" directory.
For example: /home/.blahblah/username/old.domain.org/ ends up being inside the URL of the Media item, and I can't change it in the "Link URL" field when I "show" and item in the Media Library.
Sometimes, we change our minds, too, for where we want our media to be stored!
As of now, the only way to do this is to find the location ("guid") in wp_post in the database, I believe?