Hi Mateus,
If you have used file storing in database option and you have changed this option to storing files in file system, Kentico CMS will store new files in file system and if there is request for particular file, system will try to find the file firstly in file system. If there is no such file in file system it will try to find that file in database and then if the file exists and option storing files in file system is used, the file is copied into file system automatically.
Of course, if you don't want to replace/reupload all the files manually.
Regards, Martin