If you can't see the ExitReality button (which looks like a dark ball with an orange X cut into it) then it is most probably covered up by other buttons on your IE toolbar. The givaway for this is the presence of small arrows on your toolbar. They look like this: >>

Click on these and you will most likely see the ExitReality button.

If you can grab and move your toolbars around then you can make some more room for the ExitReality button. You might have to unlock the toolbars to do this. Right click on a toolbar and you will see the Lock the Toolbars option. Uncheck this.

You can also click Customize ... which will bring up a window where you can move your toolbar buttons around, delete buttons you don't use etc.