How do I stop access to my email from a remote computer where I forgot to sign out?

We run Windows 7 on our Dell computer and use Microsoft Windows Live.  I would like to be able to access my Live email from a remote computer, but do not know how.  The computer and the Live was set up for us by another person and we are not aware of any sign-ons or passwords to allow us remote access.  Sorry not very computer literate.