View file modules/users/settings.php

<?php
$title_main = $lang['settings'].' - GOload '.$lang['title'];
require_once SYS.'/header.php';

if (!isset($user)) {
    go('/');
}

echo '
		<div class="block col-md-8">
			<h6 class="round_title">
				<a class="left" onclick="window.history.back();">
					<img src="/assets/img/left.svg" alt="back">
				</a>
				<div class="title back"><a href="/">'.$title.'</a> | '.$lang['settings'].'</div>
			</h6>

';


if (isset($_REQUEST['submit'])) {
$login = input($_POST['login']);

if ($db->query("SELECT * FROM `users` WHERE login = '$login'")->num_rows) {
	error($lang['busy_login']);
}
if (mb_strlen($login) < 3) error($lang['err_small_name']);
if (empty($login)) error($lang['err_enter_name']);

$db->query("UPDATE `users` SET `login` = '$login' WHERE `id` = '".$user['id']."'");
	go('/profile');
}


echo '
			<div class="view line menu">
				<form method="post" action="">
					Сменить логин: <br> <input type="text" name="login" placeholder="Введите новый логин" maxlength="50"> <br>
					<input class="btn" type="submit" name="submit" value="Save">
				</form>
			</div>
';

echo '
		</div>
';

?>