Delete a video clip at YouTube.

1. Log in as you.
2. Go to the https://www.youtube.com URL for the video clip, or really go to any of your video clips.
3. Click the "EDIT VIDEO" button at the lower right of the video itself.
4. Click "VIDEO MANAGER" at the upper left.
5. You will see a list of your videos each with "Edit" next to them and a down arrow by "Edit" which should be clicked to reveal the "Delete" option.
6. Delete as need be.

 
 

Addendum 12/8/2018: I don't know if what is above is any good anymore. I think you should log in as you, go to your video clips (maybe with the "My Channel" option from the dropdown menu that comes out of your avatar at the upper right), click on the video clip in question, and then the "EDIT VIDEO" button at its lower right. Finally, there is an icon that looks like three dots in a vertical line at the upper left. There is an option for "Delete" inside of the "Options" menu that folds out of this thing.