how do i delete unwanted photos from my iPhone 6s

Depends on how they got there. If they were sync'd via iTunes, then you would remove them the same way. Go to iTunes, click on the Photos option, uncheck the albums/photos you no longer want on the device.

If you are referring to something else, can you be more specific as to where the photos you want to delete reside (what album), and how they got on your device?

Cheers,

GB