Want to unlock Administrative privledges

I have a computer which was sent to me with administrative privledges still in place on it so I cannot upgrade Flash or any other program. I cannot get in touch with the person who has the administrative password as he has moved overseas.

I am trying to figure out a way I can have the administrative privledges removed so I can upgrade the computer. Currently it will not let me upgrade anything due to the admin privledges in place.

Can anyone advise how I can do this as the computer is extremely limited now. Im running windows 2000.