<select name="type" id="tip">
   <option>seçiniz</option>
   <option value="1">Dosya</option>
   <option value="2">Yazı</option>
</select>
<br>
<input id="hop" type="text" name="password" />
<script type="text/javascript">
	$("#tip").change(function(){
		if($("#tip").val() == 1){
			document.getElementById('hop').type = 'file';
		}else if($("#tip").val() == 2){
			document.getElementById('hop').type = 'text';
		}
	});
</script>