I can't delete photos from iPhone 5c I have copied to my PC

For some reason I can longer delete photos from my iPhone (while it's connected to my PC) after I copy them to my PC hard drive. I can delete them 1 by 1 directly on the iPhone but cannot no longer delete them all at once (like I used to be able to) in the window that they pop up in while connected to my PC via USB. I prefer to do it this way so I can delete all of them in 1 click instead of 1 by 1 on the phone. I am told there is some type of setting on my phone I need to change but don't what it is? Please help.