用root身份登入 进入mysql库 修改user表即可。

操作如下：

D:MySQLin>mysql -uroot -proot

Welcome to the MySQL monitor. Commands end with ; or g.
Your MySQL connection id is 391
Server version: 5.0.51b-community-nt-log MySQL Community Edition (GPL)

Type 'help;' or 'h' for help. Type 'c' to clear the buffer.

mysql> use mysql;
Database changed
mysql> update user set user='xly' where user='root';
Query OK, 2 rows affected (0.00 sec)
Rows matched: 2 Changed: 2 Warnings: 0

mysql> flush privileges;

mysql> select user,host,password from mysql.user;
+------+-----------+-------------------------------------------+
| user | host | password |
+------+-----------+-------------------------------------------+
| xly | localhost | *81F5E21E35407D884A6CD4A731AEBFB6AF209E1B |
| yxl | localhost | *23AE809DDACAF96AF0FD78ED04B6A265E05AA257 |
| xly | % | *6BB4837EB74329105EE4568DDA7DC67ED2CA2AD9 |
+------+-----------+-------------------------------------------+
3 rows in set (0.00 sec)