for a form top be able to upload a file, it's encoding type must be set to multipart/form-data.
change
<form action="newsUpdate.php?contentID=<?php echo(rawurlencode($row_WADAcontent['contentID'])); ?>" method="post" name="WADAUpdateForm" id="WADAUpdateForm">
to:
<form action="newsUpdate.php?contentID=<?php echo(rawurlencode($row_WADAcontent['contentID'])); ?>" method="post" enctype="multipart/form-data" name="WADAUpdateForm" id="WADAUpdateForm">