what should I do if I want to delete some photos that I just added from windows pc to my iphone ?

You must do it from the computer. Directions here: Sync photos from your computer to your iOS device using iTunes - Apple Support

If you put them on the phone by using iTunes to sync from a computer, you delete them by using iTunes to sync again, but with a different selection of which photos to sync to the phone. Each time you sync, iTunes sets the synced photos on the phone to match the current iTunes settings. More info from Sync photos from your computer to your iOS device using iTunes - Apple Support is copied and pasted below:

Delete synced photos

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.