Datatable updating

How do I update a datatable ?for ($i=0;$i -le $datatable.rows.count;$i++)
{
   $therow=$datatable.rows[$i]
  $therow.Servername = $SQLServer
 }

but there is some problem ..

Property 'Servername' cannot be found on this object; make sure it exists and is settable.
At line:52 char:11
+   $therow. <<<< Servername = $SQLServer
    + CategoryInfo          : InvalidOperation: (Servername:String) [], RuntimeException
    + FullyQualifiedErrorId : PropertyNotFound