How To Change the Password of Another User Account? - MySQL FAQs - Managing User Accounts and Access Privileges

If you want to change the password of someone else's user account, you can connect to the server as "root" and use the "SET PASSWORD FOR userName ..." command to change the password of another user account. There are two ways to use this command to set a new password and store it in an encrypted format:

SET PASSWORD FOR userName = 'encryptedPasswordString';
SET PASSWORD FOR userName = PASSWORD('passwordString');

Notice that PASSWORD() is a system function to encrypt the specified password. Here is good tutorial exercise to show you how to set a new password:

>cd \mysql\bin
>mysql -u root -pretneciyf mysql

mysql> SET PASSWORD FOR dev = 'iyf';
ERROR 1372 (HY000): Password hash should be a 41-digit 
 hexadecimal number

mysql> SET PASSWORD FOR dev = PASSWORD('iyf');
Query OK, 0 rows affected (0.00 sec)

mysql> SELECT User, Password, Shutdown_priv FROM user;
+------+-------------------------------------------+-----+
| User | Password                                  | ... |
+------+-------------------------------------------+-----+
| root | *3735F1D8464342BA852E10101E55E422EBAAAF35 | Y   |
| dev  | *446BD97F308FBA0B9CBDC962C2842AD338BCE59E | N   |
+------+-------------------------------------------+-----+
2 rows in set (0.00 sec)