in iTunes how to delete photos on iphones 4s

How did the photos get onto the phone ? If they were synced from a computer then they are deleted by changing your photo sync options on the phone's Photos tab when connected to your computer's iTunes and resyncing ; if you want to delete all synced photos then select an empty folder on the Photos tab and sync that.

Syncing and deleting synced photos : Sync photos from your computer to your iOS device using iTunes - Apple Support