Tips on Customizing Ledenbeheer

How to Hide Ledenbeheer Admin Menus

function plt_hide_ledenbeheer_external_connection_menus() {
	//Hide "Settings → Ledenbeheer".
	remove_submenu_page('options-general.php', 'ledenbeheer');

	//Hide "Ledenbeheer".
	remove_menu_page('ledenbeheer');
	//Hide "Ledenbeheer → Courses".
	remove_submenu_page('ledenbeheer', 'edit.php?post_type=courses');
	//Hide "Ledenbeheer → Activities".
	remove_submenu_page('ledenbeheer', 'edit.php?post_type=activities');
	//Hide "Ledenbeheer → Profielen".
	remove_submenu_page('ledenbeheer', 'users.php');
	//Hide "Ledenbeheer → Instellingen".
	remove_submenu_page('ledenbeheer', 'options-general.php?page=ledenbeheer');
}

add_action('admin_menu', 'plt_hide_ledenbeheer_external_connection_menus', 11);

Where do I put this code?

How to Hide Ledenbeheer Meta Boxes

function plt_hide_ledenbeheer_external_connection_metaboxes() {
	$screen = get_current_screen();
	if ( !$screen ) {
		return;
	}

	//Hide the "Contact info" meta box.
	remove_meta_box('profiles-meta-box', $screen->id, 'normal');
	//Hide the "Cursus info" meta box.
	remove_meta_box('courses-meta-box', $screen->id, 'normal');
	//Hide the "Extra activiteit info" meta box.
	remove_meta_box('activities-meta-box', $screen->id, 'normal');
}

add_action('add_meta_boxes', 'plt_hide_ledenbeheer_external_connection_metaboxes', 20);