How to edit "Your Message has been sent" message on contact form blogger

Question

Include the following code snippet within <head></head>:

<script src='//code.jquery.com/jquery-latest.js'></script>
<script type='text/javascript'>//<![CDATA[
$(function(){
  $('.contact-form-button-submit').click(function(){
    $('.contact-error,.contact-success').hide();
    var email = "Cowboy! Provide the correct E-mail.";
    var description = "Whats your problem Sir write in description box.";
    var success_msg = "Success";
    if($('.contact-form-error-message-with-border').text()=="A valid email address is required."){
      $('.contact-form-error-message-with-border').replaceWith("<div class='contact-error'>"+email+"</div>");
      $('.contact-form-error-message-with-border').hide();
    } else if($('.contact-form-error-message-with-border').text()=="Message field cannot be empty."){
      $('.contact-form-error-message-with-border').replaceWith("<div class='contact-error'>"+description+"</div>");
      $('.contact-form-error-message-with-border').hide();
    } else {
      // success case
      $('.contact-error,.contact-success').html(success);
    }
  });
});
//]]></script>

email is the error message for email, while description is the error message for message.

Note: this original snippet is from here (Author: Mohammad Hamza Dhamiya), success message modification added.