To hide the top menu, simply select 'Hide Top Menu' under the 'View' option in the main menu, located near the top of the SpreadsheetLIVE user interface. Once it is hidden, the option will change to 'Show Top Menu', if you decide that it's preferable to see the top menu. It is highlighted below.
Image 1 - The 'Hide Top Menu' option under the 'View' option in the main menu and the top menu highlighted in the user interface.