If you're checking your upload before confirming it, just indicate that the upload was bad on the confirm page and the local download will be deleted. If you just confirmed it without watching the server version (a step that could have saved you this problem), you need to put in a deletion request to get rid of the local copy.
At the bottom of the
edit videos page is a link to put in a
deletion request. Select the video that you want the local download deleted for, and put your explanation in the "Reason for deletion" box, specifying that you only want the local download deleted, not the video entry itself. After this request is processed, you'll be able to re-request upload permission.
hth,
--K