It is your broswer that controls whether you are "logged in" to the CAHSEE site. Consequently, there is no direct way for this site to force you to "log out".

Method 1

One method is to simply quit your browser; that should log you out.

Method 2

Alternatively, there is a somewhat roundabout method that causes most browsers to forget your login information; if you want to try that,

click here.
This will pop up a new login dialog.