Navigate to your 'My Media' page. You will see your media
arranged in a list. On the right side of the page, each entry will
have a pencil icon 'Edit' button. Select this to edit the media. You will
also find an edit button on any of page where you can view media that
you own. It will be below the video on the right, in the 'Actions'
Select the "Replace Video" tab.
Click '+ Choose a file to upload' and select the file with
which you want to replace the current media.
Wait for the new media to upload.
After the media has uploaded you will have the option to
cancel or approve replacement. If you choose to cancel, the original
media will not be replaced. If you approve the replacement, the new
media will replace the original once the new media finished
transcoding. Note: The original media is not recoverable once
replacement has been approved.