i use a program called "duplicate file finder". scans a folder (and its subfolders) for exact duplicate files, recognised by file size, and automatically selects them, so all you have to do is push the delete button there and the files are moved to recycle bin. very quick and easy to use.
now this method deletes a lot of duplicates, but not all.
there are cases where you have the same image or video, but different file sizes or resolutions, which still need manual detection and deletion.