How to delete photos in your iPhone photo library?

I just got the iPhone and they guy at the Verizon store transferred all of my photos from my old droid to this new iPhone. The problem is, photos I've never taken and some that randomly got there from Tumblr got mixed up with my photos. I want to delete some of them, but there's no little trashcan in the bottom. What do I do?

You either click on the photo and a trash can should be on the top right corner one by one or you can delete them all in couple touches by clicking edit and selecting all the photos to delete, and then there should be a red thrash can to click on