How to delete duplicates

Do the opposite of what you suggest: Command+click the ones that you want to keep. Then copy them to a new location and delete the old folder's contents.

If everything that is duplicated shares a common naming structure and you don't want to do the manual method above, you can use Automator to write a script, but you'll have to do a little coding. Automator is an Apple program already installed on your computer in the Apps folder or the Utilities folder.