Enterprise Manager Configuration Assistant - Oracle 10g/11g Data and Database Management Utilities - page 357

Changing SYSMAN password
The procedure to change the password starts with properly setting the environment
variables: ORACLE_HOME , ORACLE_SID , and PATH.

1. Shut down Enterprise Manager Console and make sure it is completely off.
emctl stop dbconsole
emctl status dbconsole

2. From a SQL*Plus prompt connected with a privileged account (SYS, SYSTEM
or SYSMAN) modify the SYSMAN 's password with a regular ALTER USER
command
SQL> alter user SYSMAN identified by <SysmanNewPassword> ;

3. Verify you can open a SQL*Plus session using the SYSMAN user identified
with the recently set password.
sqlplus SYSMAN/<SysmanNewPassword>

4. The next phase has to do with replicating the change on the EM configuration
files.

5. From an OS prompt change the current directory to <Oracle Home>/

<Hostname>_<Oracle SID>/sysman/config directory.

6. Backup the emoms.properties configuration file.
7. Edit the emoms.properties file with a text editor, look for the oracle.
sysman.eml.mntr.emdRepPwd entry and replace the text string with the new
SYSMAN password written in clear text, then look for the oracle.sysman.
eml.mntr.emdRepPwdEncrypted entry and change the value to FALSE .
Enterprise Manager will automatically change the value to TRUE and it will
rewrite the password with the encrypted version.
8. Once you are ready, start the console using the regular emctl start
dbconsole command and when this step is finished verify the password
written in the previously modified configuration file has changed to the
encrypted version.
Your Enterprise Manager console should be up and running now with the new
password. You can verify the access of the SYSMAN user sessions in the database
with a simple query to the V$SESSION dynamic view.