Application Control Maximize expands the active application window to the full size of the screen. Document Control Maximize expands the active document window to the full size of the application window. To restore a maximized window to its former size, use the Restore command.
To maximize the window:
Click the icon in the upper left corner of the title bar and select Maximize
Or right-click the title bar and then click Maximize
Or click 
Or right-click the window title bar and then click Maximize
Or press ALT+SPACEBAR+X (application) or ALT+HYPHEN+X (document)