Delete images/videos is very easy. Simply go to the project you'd like to edit. Located at the top-right is a edit "cog" icon.
From the dropdown menu select Edit Media.
After the Edit Media page loads, you will have access to all the images and videos that exist on your project page.
Click the trashcan icon to delete the row you don't want anymore.
Your page will be auto updated, so no need to save anything.