how to delete a file from folder in php

No need of while loop here for just deleting a file, you have to pass path of that file to unlink() function, as shown below.

$file_to_delete = 'items/item2.txt';
unlink($file_to_delete);

Please read details of unlink() function

http://php.net/manual/en/function.unlink.php

There is one bug in your code, you haven't given the correct path

<?php
        $data="item2.txt";    
        $dir = "items";    
        $dirHandle = opendir($dir);    
        while ($file = readdir($dirHandle)) {    
            if($file==$data) {
                unlink($dir."/".$file);//give correct path,
            }
        }    
        closedir($dirHandle);

?>    

• unlink

Initially the folder should have 777 permissions

$data = "item2.txt";
$dir = "items";
while ($file = readdir($dirHandle)) {
    if ($file==$data) {
        unlink($dir.'/'.$file);
    }
}

or try

$path = $_SERVER['DOCUMENT_ROOT'].'items/item2.txt';
unlink($path);