Open the Photos app
Tap Library, Albums, or Recents
Tap Select
Tap the photos you want to remove
Tap the Trash icon
Tap Delete Photo
To remove photos from an album only, open the album
Tap Select
Tap the photos
Tap Remove from Album
To delete photos from iCloud and all synced devices, make sure iCloud Photos is enabled
To recover deleted photos, open Albums
Tap Recently Deleted
Tap Select
Tap Delete All or Recover