How to delete videos

I have just spent 3 hours listing one item on eBay! Why? Because every time I loaded more than two photos from my gallery, a video automatically started playing using up data and I got a message saying I did not have enough memory. I do not know where the video came from and I would like to delete it. I cannot figure out how to get to it. It appears on the gallery screen where I go to access my camera to select photos. Please help!