The Registered Owner Information does not affect who can and can't access files on the laptop, so I'm not too sure what you are referring to.
Are you saying that you can't access anything for lack of the correct password, or you just want to change the Registered Owner Information?
Assuming it's the latter, go here: http://www.howtogeek.com/howto/windows-vista/quick-tip-change-the-registered-owner-in-windows/