Solution 1 :

Problem solved...

/*Change text strings */
function my_text_strings( $translated_text, $text, $domain ) {
    switch ( $translated_text ) {
        case 'Subtotal' :
            $translated_text = __( 'Your text here', 'woocommerce' );
            break;
            case 'Checkout' :
            $translated_text = __( 'Your text here', 'woocommerce' );
            break;
            case 'Show Cart' :
            $translated_text = __( 'Your text here', 'woocommerce' );
            break;
    }
    return $translated_text;
}
add_filter( 'gettext', 'my_text_strings', 20, 3 );