Just click on the Stop Google Web Accelerator menu item. Note that when Google Web Accelerator is turned off, the Google Web Accelerator icon in the system tray goes away. To restart Google Web Accelerator, either go to the Google Web Accelerator Toolbar menu and click Start Google Web Accelerator or select Google Web Accelerator in your Windows Start menu.
If you've made the Google Web Accelerator Toolbar invisible in IE, to access its icon menu you'll have to make it visible again by clicking on View > Toolbars > Google Web Accelerator from your main browser menu toolbar.
From this link:
http://webaccelerator.google.com/support.html# off1