Hello,
Thanks for reaching out for support! I understand you’re trying to replace your previous carousel video with an updated version, but you’re unable to figure out how to do so. I’m happy to help!
For any image or video that you’d like to adjust, you can delete them from the Dev Sandbox and add a new piece of media in its place. Based on what I’m seeing, it looks as though you were able to update this already. Nice work! Let us know if you have any additional questions!