Q: deleting aperture without deleting external hard drive photos

I am trying to free up space on my hard drive.  I have both aperture and photos.  I am trying to get rid of aperture, it crashes all the time.  I have 66000 photos on it.  I have backed up my photos from aperture and Photos to two external hard drives.  When I delete a photo from my hard drive it is deleting it from my external as well.  How do I make sure that doesn't happen?  I have way too many photos to lose.