Just create a file "new_password.php" (or with any other name) inside your drupal folder and access it using browser. It will generate one way encrypted hash password for you.
<?php
define("DRUPAL_ROOT", getcwd());
require_once DRUPAL_ROOT . "/includes/bootstrap.inc";
drupal_bootstrap(DRUPAL_BOOTSTRAP_FULL);
require_once "includes/password.inc";
echo user_hash_password("123456");
die();
menu_execute_active_handler();
?>
When you run this code in browser it will show you hash password like
$S$D95YW4EejaUDPq5nZ7Z2Ljx1Ud4wlN1iTMQdAKton70JcQpCZmrG
Now you need to update your database table using above hash. Open your database using PHPMyAdmin or Workbench and run the below query.
UPDATE users SET pass = '$S$D95YW4EejaUDPq5nZ7Z2Ljx1Ud4wlN1iTMQdAKton70JcQpCZmrG' WHERE uid = 1;
Now you can access drupal using username as "admin" and password as "123456". Make sure you update password after login to the admin.