How to delete or remove an image to an auto inserted gallery
When using the Automatically Insert Gallery or Sliders extension, gallery management is pretty much automatic. However if you are not importing listings and want to manually remove an image from a listing do the following.
Edit the listing you want to remove the image from and press the Add Media button.
Select > Uploaded to this post option to only display the images attached to this listing.
Now you will get a list of images attached to this listing.
Select the image you want to delete and press Delete Permanently.
Detach image from listing an alternative to deleting
Visit Dashboard > Media and press the list view style.
Note: This way works best when you have pre-named the images prior to upload.
Search for the image and press Detach.