SQL Guide : Using SQL for database administration : Managing user privileges and roles : Changing a password
  
Changing a password
You can change your password with the ALTER USER command. Administrators can also change passwords of other users.
Procedure
Use the following syntax to change the password of a given user:
ALTER USER username IDENTIFIED BY new_password
Example
The following statement changes the password of the user CALVIN to GUBBES
ALTER USER CALVIN IDENTIFIED BY GUBBES
Related tasks:
Changing administrator's user name and password
See also
Managing user privileges and roles