Delete videos from iMovie media

I have imported videos from iTunes to my iPhone and now would like to delete them from iMovie Media. There is no copy in my Photos so I figured I can only see them in iMovie. I clicked on the video that I want to delete but there is no edit/manage/delete buttons for me to delete those videos. I tried to create a new project and went to iMovie media but still does not have any delete options. Is there any way to delete them from iMovie media? (iMovie version: 2.2.5)