How to delete duplicates

I have a bunch of .m4a files that I recorded on my iPhone voicememo, but there are more than 20 copies for the same one for some reason. How can I delete every thing except one copy, without having to tediously delete it by click on 2nd duplicate, press Shift, click on the last duplicate, delete?

I have some .mp3 duplicates that I would like to delete as well.

 

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.