I having problem. i have few collection of lightroom catalog from my past work.Now i want to merge all catalog's into one and delete rest of all except keeping that one fresh. But i am confused, is it safe to deleted all catalogs and there will be no need of old catalogs anymore.. and how to do it with lightroom 5.
It's perfectly safe to do. Lightroom is non-destructive. All the details about changes are stored in the lrproj files. Once you have moved the data you need out of the lrproj file, there is no reason you need to keep the old lrproj or any of the cached files around, so long as you keep the original image files on which the catalog depends.
To avoid making errors, I suggest renaming the files and folders that you think you can get rid of and then checking for missing images in your new project. As long as everything works correctly, you then know it is safe to remove the files you renamed.
As I began to use Lightroom for much of my photographic work, I began to hate the LR catalogs. So here's a hybrid workflow that I think you may find better for large archives and libraries.
Simply make a new catalog for each event. Since I shoot many hundreds of images at an event, creating one large LR catalog slows down my whole workflow. Making one per event allows me to work quickly and keep multiple catalogs that are small and purpose built.