John Godley

Enhances the WordPress media library by allowing you to rename the underlying media files. Any change to a media item’s title will result in the media filename also being changed.
See the screenshot for more details of where to rename media files.
Note that all thumbnails will also be renamed. If you are using a caching plugin, such as WP Super Cache, then you will need to clear your cache so that any references are updated. This plugin does not update existing direct links to files (links inside a WordPress gallery will change).

Rename Media

Rename underlying media files from the WordPress media management interface

Jordy Meow

Rename the alternative text of your media easily directly using the Media Library, without a click.
BETA. This plugin was just created. I am waiting for the first feedbacks of my users to decide which way to go. The first thing I will implement is to update the ALT in the POSTS.
BE KIND. Again, this plugin is new. Please help us 🙂
More information available on http://apps.meow.fr/media-alt-renamer/.
<h4>Quickstart</h4>
<ol>
<li>Check the Media Library, in list view (not grid view).</li>
<li>Modify the Alt Text field, and simply type ENTER when it’s done.</li>
</ol>

Media Alt Renamer

Rename the alternative text of your media easily directly using the Media Library, without a click.

Rename Media vs Media Alt Renamer