Q: I can't delete old photos off my iPhone (unless I do it manually)

It depends on where the photos came from. If your photos are in Camera Roll, i.e., photos you took with your own phone, you can just go to Photos > Camera Roll > Edit > Select and then rub your finger across multiple photos to select a large batch. Then delete.

If your pictures were synced to your iPhone from your computer using iTunes, you would have to go back to iTunes and re-sync with no folders selected.

If you have iCloud Photo Library enabled then check this:

iCloud Photo Library FAQ - Apple Support

You are trying to delete photos from an iPhone, correct? If so don't go to iTunes. Just follow what I suggested. On your phone:

Photos > Albums Tab at bottom > Camera Roll > Select and then rub your finger across multiple photos to select a large batch. Then delete.

You can select a large batch by rubbing your finger making it a little easier.

Alternatively do you have PC? On a PC, open File Explorer, look on the folders on the left side, you should see the iPhone as a camera, expand the subfolders and the photos should appear under the DCIM folder(s) (there may be more than one). This is not possible on a Mac.

Also to confirm, you are not using iCloud Photo Library, correct?

Did you try deleting them with File Explorer on a PC?

I usually use File Explorer to delete photos, and it says I do not have permission.  I can't figure out what setting I need to change to allow me to delete.  I JUST got an iPhone6s.  On my old phone (a 5) I was always able to delete using file explorer.  Any help would be appreciated. Thanks.

Try this. If no help it might be best to open a new thread and describe your phone settings and error messages.

cannot delete you do not have permission to delete this item

THANK YOU!  Turning off the iCloud library worked!

You are welcome.