Q: i copy some pic from computer to iphone 6 and now i want to delete but icant how i  can do it

IF you synced the photos from the computer using iTunes, you have to remove them from the phone using iTunes.

Sync photos from your computer to your iOS device using iTunes - Apple Support

1. In iTunes, locate and click on your device.
2. Click Photos.
3. Choose "Selected albums" and deselect the albums or collections you want to delete.
   To delete all synced photos, deselect "Sync Photos from" and, when asked, click "Remove photos."
4. Click Apply.

Learn how to delete photos and video synced from iTunes when you can't access the originals.