Print/debug cause of upload error in PHP - php

Question

I'm a PHP newbie and have written a script to process form uploads. It works for small files(less than 1Mb). However when I try to upload an ~4Mb pdf file it returns an error message. What am I doing wrong?
PS: I ran php_info, got the value of "upload_tmp_dir" and set it to a directory owned by the apache process(www-data)
My client-side code is
<form action="upper.php" method="post" enctype="multipart/form-data">
<input type="file" name="myFile"><br>
<input type="submit" value="Upload">
</form>
Upper.php contains
define("UPLOAD_DIR", "/var/www/html/upload/");
if (!empty($_FILES["myFile"])) {
$myFile = $_FILES["myFile"];
if ($myFile["error"] !== UPLOAD_ERR_OK) {
echo "Error is " . $myFile["error"];
//echo "<p>An error occurred.</p>";
exit;
}
$name = preg_replace("/[^A-Z0-9._-]/i", "_", $myFile["name"]);
// don't overwrite an existing file
$i = 0;
$parts = pathinfo($name);
while (file_exists(UPLOAD_DIR . $name)) {
$i++;
$name = $parts["filename"] . "-" . $i . "." . $parts["extension"];
}
// preserve file from temporary directory
$success = move_uploaded_file($myFile["tmp_name"], UPLOAD_DIR . $name);
if (!$success) {
echo "<p>Unable to save file.</p>";
exit;
}
// set proper permissions on the new file
chmod(UPLOAD_DIR . $name, 0644);
}

Answer 1

Most probably you have wrong config in you php.ini file.
You need to set
; Maximum allowed size for uploaded files.
upload_max_filesize = 40M
; Must be greater than or equal to upload_max_filesize
post_max_size = 40M
its already described here: PHP change the maximum upload file size

Answer 2

You ned to set values in php.in file.
Open the file,
Find upload_max_filesize and post_max_size lines.
Change this two value. (M= MB)
; Maximum allowed size for uploaded files.
upload_max_filesize = 20M
; Must be greater than or equal to upload_max_filesize
post_max_size = 20M
Restart the sever for effect.
Note:
You can set any number. But not use any decimal value.
Open the php.ini file in NOTEPAD. Don't user wordpad or any word processor.