How to Hide Next Watermark Admin Menus

function plt_hide_next_watermark_menus() {
	//Hide "Next Watermark".
	remove_menu_page('nwm-acp');
	//Hide "Next Watermark → Next Watermark".
	remove_submenu_page('nwm-acp', 'nwm-acp');
	//Hide "Next Watermark → General Settings".
	remove_submenu_page('nwm-acp', 'nwm-acp&tab=wm_settings');
	//Hide "Next Watermark → Watermark Text".
	remove_submenu_page('nwm-acp', 'nwm-acp&tab=wm_text');
	//Hide "Next Watermark → Watermark Image".
	remove_submenu_page('nwm-acp', 'nwm-acp&tab=wm_image');
	//Hide "Next Watermark → Backup/Restore".
	remove_submenu_page('nwm-acp', 'nwm-acp&tab=wm_media');
}

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

Where do I put this code?