Edit query_post onchange select box()

I’m New to WordPress

In category page, i have select box for change the posts by authors in that category

My select box

<select name="sortByAuth">
<option value="0">By Author</option>
<?php
$authors = get_users('role=author');

if(isset($authors) && !empty($authors)) {
foreach($authors as $author) :
?>
<option value="<?php echo $author->ID; ?>"><?php echo $author->display_name; ?></option>
<?php
endforeach;
}
?>
</select>

Now i want posts by selected author from select