Renaming files is a difficult (and actually, impossible) with WordPress, but Media File Renamer makes it really easy. I recommend you to be first used to the Auto-rename method, which is the standard way of using this plugin.
With WordPress, modifying files is a dangerous process. Please prepare a backup before doing anything (BlogVault is recommended), then rename a few files at first.
There are three ways of renaming your files automatically.
By changing the title
In the Edit Media screen, as you probably already now, there is the title of your media entry. If you change this and hit Update, the file will be also renamed.
A new column in the Media Library will be displayed. By default, Media File Renamer recommends you an ideal filename based on the title of this media.
By the Renamer Dashboard
If you are interested in renaming all the files at once, you can do it through the dashboard of Media File Renamer. Before doing that, make sure everything works properly if you do it one by one first. It’s highly recommended to make a backup before going forward.
Other Auto Methods
The Pro version brings two more methods to rename files automatically.
Attached Post Title
If you attached your Media entries to a particular post (page, product, or anything else), then you can have them renamed based on the title of that post. It’s commonly used by users of WooCommerce who like to have their products named after the product’s title.
Sometimes, there are the titles you would like to display to your visitors, and a more descriptive (but not long) titles that you would like to use for SEO purposes. The Alternative Text is useful for that, and SEO experts love it. Media File Rename can take advantage of that way of doing this, and give nice filenames based on those values.
Lock and Unlock
By clicking on the button, the files will be renamed directly. You can lock or unlock this automatic process by using those little icons.
This allows you to organize your renaming tasks efficiently.
The Pro version was created almost two years after the first release of the Free version. It adds requested features, such as the Manual Rename. You can edit the filenames of your Media directly, through the Media Edit screen or through the Media Library.
Please note that manually renaming a file will set the renaming into locked. That will prevent the plugin to rename this media entry again, if you change its title for example. Thanks to this, you can use both the Auto and Manual renaming together, to your advantage.
If you need to customize or trigger the renaming, you can. There are many filters and actions you can use. Have a look at the Questions & Issues.