operatingsystem password

Ask the admin or read the documentation from the installation.
Anything beyond that would be considered hacking/cracking and (in general) can't be discussed in these forums.

What, specifically, is the problem you're facing?

here is the issue..my pc is running fine..
 it is easliy going to windows with out asking user name and password...
but in my oracle software it is asking os username and password..
please help me ..

If it's Windows, and you forgot what you put in for the autologin, just launch the Task Manager (ctrl-shift-esc).  Go to the "Users" tab and it will show you the active logins.  If you're already logged in, then you can change your password.

Not sure why you wouldn't know your own username and password, but I guess it could happen.  I see this often when people "inheiret" a computer where the original owner left everything with an automatic login.

For your own safety, turn off automatic login.  All it does is make your computer more useful to a thief.  And, it makes people forget their own names and passwords.  :)

I saw it I right clicked and logoff then can I change the password or not