I can see that the File class has updateLinks() [url]http://api.silverstripe.org/default/File.html#updateLinks[/url] - but can't find any way to update the actual filesystem file via the Files & Images admin and then fire off this updateLinks() for the selected File entry in the db.
Once an admin has a bunch of links everywhere directed to a particular File, if they need to update the pdf (for example) they have to upload a new File via the admin and then go to all the pages referring to the old File and change the links.. ? That can't be right can it?
This functionality is part of the versioned files module - you can grab it from http://github.com/ajshort/silverstripe-versionedfiles. In the Filest & Images area, when you click on the edit button for a file a new Replace tab will show up.