Nicolas Gasparato wrote a rather thorough article on the subject of user password, and mostly, I just want to capture a bookmark to it on my blog:
The best way that I have found to change the SYSADM password (the database user that PeopleSoft uses to connect) is to use Data Mover and the change_access_password command.
You can read the official documentation on the command here:
The syntax looks something like this:
change_access_password SYSADM1 <new password>;
The first parameter is the Symbolic ID. While it is probably SYSADM1, you can read it from the PSACCESSPRFL table:
select * from PSACCESSPRFL
The second parameter is the new password that you want to use.
The command will both change the password in the database and change the place where PeopleTools stores the password to use when connecting. You will still probably still want to clear the cache and restart the servers including app, batch, and web.