how can i upload image on button click using ajax and php

$(".save").click(function()
{
      var first_name = $("#fname").val();
      var last_name = $("#lname").val();
      var password = $("#new_pass").val();
      var email = $("#new_email").val();
      var profile_pic = $_FILES["profile_pic"]["name"];
      $.ajax({
             url:"<?php echo base_url() ?>index.php/home/update_profile",
             type:"POST",
             data:      
             {    
              fname:first_name,lname:last_name,newpass:password,newmail:email,profile_pic:profile_pic
           },
           success:function(result)
           {
                 alert(result);
            }
       });
 });

here i'm not getting the path for selected file
but i want to transfer file to server using php