Resize an image whilst uploading

<?php
$user=$_SESSION['dbUser']['username'];
$db=new mysqli('host','username','password','database');
if($db->connect_errno){
echo $db->connect_error;}
$pull="select * from users where user='$user'";

$allowedExts = array("jpg", "jpeg", "gif", "png","JPG","PNG");
$extension = @end(explode(".", $_FILES["file"]["name"]));
if(isset($_POST['pupload'])){
if ((($_FILES["file"]["type"] == "image/gif")
|| ($_FILES["file"]["type"] == "image/jpeg")
|| ($_FILES["file"]["type"] == "image/JPG")
|| ($_FILES["file"]["type"] == "image/png")
|| ($_FILES["file"]["type"] == "image/pjpeg")
|| ($_FILES["file"]["type"] == "image/PNG"))
&& ($_FILES["file"]["size"] < 200000000)
&& in_array($extension, $allowedExts))
  {
  if ($_FILES["file"]["error"] > 0)
    {
    echo "Return Code: " . $_FILES["file"]["error"] . "<br>";
    }
  else
    {

    echo "Uploaded Successully<br>";
    echo "It may take up to half an hour to update.<br><br>";

    if (file_exists("upload/" . $_SESSION['dbUser']['username']))
      {
      unlink("upload/" . $_SESSION['dbUser']['username'].".".$ext);
      }
    else
      {
          $pic=$_FILES["file"]["name"];
            $conv=explode(".",$pic);
            $ext=$conv['1'];

      move_uploaded_file($_FILES["file"]["tmp_name"],
      "upload/" . $_SESSION['dbUser']['username'].".jpg");
      $url=$user.".jpg";
    
      $query="update picture set url='$url', lastUpload=now() where user='$user'";
      if($upl=$db->query($query)){
		header('Location: ' . $_SERVER['HTTP_REFERER']);
              }
      }
    }
  }
else
  {
  echo "File Size Limit Crossed 200 KB Use Picture Size less than 200 KB";

  }
}
?>