Lr CC manages the cache intelligently. So your originals will drop out of storage automatically unless images are actively being worked on/ edited. However you can delete originals manually if everything is backed up in the cloud.
Preferences >> Local Storage
Click the browse button next to your nominated storage location and find the folder Lightroom CC. Inside that folder you should find another with a long string of letters and numbers. Double-clicking opens the originals folder. The year folders will contain dated sub-folders and then image files. You can delete the year folders e.g. 2014, 2015, 2016 2017 etc. That will leave the Originals folder empty.
You need to explain what you are trying to achieve.
when you are working with Lightroom Classic CC you original files are stored on your computer system e.g on your HDD, external HDD or network connected HDD.
The new Lightroom CC copies your original files to web storage in the Adobe Creative Cloud.
Which image file storage you wish to delete, the Cloud storage or the Storage on your computer system?
I assume the files in Lr Classic will be kept in their regular folders as an archive or local backup in addition to the originals in the cloud.
I'm keeping LR Classic catalog as my archive.
I figured out what I was doing wrong. I just needed to delete the originals folder first, then point to the new location which is an internal drive.
Quote “I'm keeping LR Classic catalog as my archive.”
Just so you are aware, the Lightroom Catalog does not contain your image files. The files are stored on your computer hard drives.
Thanks but I'm well aware. Been using Lightroom since early betas of the first version.