Implement change password in Symfony2
$builder->add('password', 'repeated', array(
    'first_name' => 'New password',
    'second_name' => 'Confirm new password',
    'type' => 'password'
));

// in action:
$oldpassword = $user->getPassword();

if ($request->getMethod() == 'POST')
        {
            $form->bindRequest($request);

            if ($form->isValid())
            {
                // check password here (by hashing new one)