how to change admin logo in wordpress

add_action(“login_head”, “my_login_head”);
function my_login_head() {
echo ”
<style>
body.login #login h1 a {
background: url(‘”.get_bloginfo(‘template_url’).”/img/_logo.png’) no-repeat scroll center top transparent;
height: 204px;
width: 400px;
margin-left: -41px;

}
</style>
“;
}

function put_my_url(){
return (‘http://mysite.com&#8217;);
}
add_filter(‘login_headerurl’, ‘put_my_url’);