Rather than change an original image, Adobe Lightroom 5 saves the location of the original image and records the edits made to it in a database called a catalog. Lightroom creates the final image by applying the recorded changes to a copy of the original image. While the catalog workflow functions well when you use the same image assets in multiple projects, catalogs take forethought to set up and problems can crop up, especially when catalogs nest inside other catalogs. Lightroom doesn't contain an in-application way to delete a catalog, but you can delete a catalog while Lightroom is closed.
Start Lightroom. Click on the "Edit" menu and select "Catalog" to open a dialog box. On Mac OS, the menus are "Lightroom" followed by "Catalog."
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Click "Show" on the General panel to open the directory that contains the catalog in Windows Explorer or Mac OS Finder.
Close Lightroom. While Lightroom is open, the operating system will not let you manipulate any files the program is using, including the catalog files you need to delete.
Delete the Lightroom-specific files from the directory. They are "catalog.lrdata," "Previews.lrdata" and "Smart Previews.lrdata." The original photos to which the files are linked are not deleted. Lightroom regenerates deleted Previews folders that are linked to other projects if the project they're associated with calls for them, which may take some time when the program starts up. If you are certain you don't need the catalog or any other assets in the folder again, delete the entire folder.