Can you help me delete imported photos from iPhone (4s) running ios 7?

I made (what appears to be) the mistake of importing photos from my PC to my new iPhone 4s using itunes. They now seem to be permanent occupants. I can select them (in the "Moments" view in the Photos app) but the trash can on lower right is always grayed out. It appears that in ios 6 they could be deleted in the Settings/General/Usage (I also synced over some music which is deletable here). Can anyone help me?