How do I delete photos ONLY on my iphone.

So I'm trying to delete all of my photos on my camera roll. When I go to my settings > usage > photos. I swipe the camera roll to reveal a delete option. When I hit the option to delete it goes back to my usage and all of the apps that are using my space. The only problem is now is that it doesn't actually delete it when I tell it to; and I can't go back into the option to swipe delete it unless I refesh the usage screen.

I've tried to manage my photos through itunes, but there's no way to actually remove the photos, only sort folders of the photos and sync them. And when I don't sync any of the folders, it doesn't unsync the photos I don't want on my phone.

Is there any way around this besides going in and deleting all 5gigs of my photos one by one?

Anything helps.