To change your database user password, execute the following SQL.
ALTER USER user_name PASSWORD 'any_password_here_in_single_quotes';
Before changing the password, make sure your database has been started.
~$ csql -u dba demodb csql> ALTER USER dba PASSWORD 'my_new_pass'; Current transaction has been committed. 1 command(s) successfully processed. csql>
Remember that in order to change a user password you need to be logged in as an admin user (or a user who has a permission to change a user password). In our case, dba is an admin user. Otherwise, you will get an error saying "UDPATE authorization failure".
Alternatively, you can set the database user password at the database creation time.