Sometimes you have sent out a link with a video to your users, or the information in a video needs to be updated. Maybe the information is outdated or the company have changed graphical profile.
In a situation like this you can replace the video content in a media by uploading a new video to replace it with while still keeping the same old links and media ID.
This can be done through Details > General > "..." and then Replace video.
This will prompt you with a warning, letting you know it will erase all previous content that is connected to the old video (video files, audio tracks, subtitles).
Accepting this will open a new window, uploading a video clip as normal.