function prepare_meta_fields( $meta_fields ) {

    $meta_fields['field_key'] = array( 'label' => 'Field Label', 'type'  => 'text', 'group' => 'wordpress');

    unset( $meta_fields['unwanted_key'] );

    return $meta_fields;

}


add_filter( 'wpf_meta_fields', 'prepare_meta_fields' );