If you find that there was an error when you uploaded a results file you can delete the file and reupload. The permission to delete results is only available to people with the full 'club administrator' permission.
Click on the delete link next to the session you need to re-upload. Confirm to say you are sure as this action is not reversible.
Once you have deleted the file, the session will show back in the list of 'sessions waiting for upload'.
(If you're an EBU club, we also delete the session from their records. Read more.)