Unregister widget with child theme

Hello,
I would like to unregister the PopularWidget with the functions.php of my child-theme and then insert my own that is based on the widget.

I currently have these lines of code in my functions.php:

function remove_last_projects_widget() {
	unregister_widget( 'PopularWidget' );
};
add_action( 'widgets_init' , 'remove_last_projects_widget' );

This however does nothing.
It is the right class name, as far as I know.
Any help would be appreciated.