Enterprise Manager Configuration Assistant - Oracle 10g/11g Data and Database Management Utilities - page 358

Changing DBSNMP password
This is the second administrative user related to Enterprise Manager and when you
need to change its password there is a procedure you must follow.

It is assumed that the ORACLE_HOME, ORACLE_SID, and PATH environment variables
are properly set.

1. Stop the standalone console:

emctl stop dbconsole

2. Verify both the console and the agents are down:

emctl status dbconsole
emctl status agent

3. Connect with a privileged user at SQL*Plus and change the DBSNMP
password:
SQL> alter user DBSNMP identified by < DBSMPNewPassword >;

4. Verify you can open a SQL*Plus session using DBSNMP and the recently
assigned password:
sqlplus DBSNMP/<DBSNMPNewPassword>

5. At the OS level change to the directory and use a text editor to modify

the targets.xml file (you must backup this file prior to proceed with the
modification).
<Oracle Home>/oc4j/j2ee/OC4J_DBConsole_<host>_<Oracle SID>/emd

6. Look for the line:

<Property NAME="password" VALUE="<encrypted_string>"
ENCRYPTED="TRUE"/>

7. Replace the encrypted value with the new password value, and the
ENCRYPTED entry value to TRUE , this will allow you to write the password
in clear text format, later EM will change this value with the encrypted
password version.
8. Finally, start the console and verify the entry you modified has been changed
to encrypted and the encryption flag is set back to TRUE .