我只是擦了擦Mac，然后重新安装了El Capitan。我正在努力连接到Mysql。通过Web服务器设置过程，我创建了一个简单的PHP测试文件：

<?php
  $conn = new mysqli("127.0.0.1", "root", "xxxxxxxx");
  if ($conn->connect_error) echo "Connection failed: " . $conn->connect_error; 
  else echo "Connected successfully";
  phpinfo();
?>

运行它时，出现以下错误：

Warning: mysqli::mysqli(): (HY000/1862): Your password has expired. To log in you must change it using a client that supports expired passwords. in /Users/rich/Documents/DESIGN/test/index.php on line 3
Connection failed: Your password has expired. To log in you must change it using a client that supports expired passwords.

我以前从未见过来自连接的响应。如果无法连接该如何解决？

编辑

在终端中，我输入了以下命令：

mysql -u root -p

这要求我输入我输入的密码（当前密码）。我现在可以访问mysql命令，但是我尝试执行的任何操作都会导致此错误：

ERROR 1820 (HY000): You must reset your password using ALTER USER statement before executing this statement.

如何使用重置密码ALTER USER？