The Layout menu contains the following commands:
3-Pane Side by Side View
Shows all three panes aligned side-by-side vertically.
Second-Third Pane View
Shows the middle and right panes only.
First-Second Pane View
Shows the left and middle panes only.
Default 2-Pane View
Hides the middle pane and displays the right and left panes only.
3-Pane Mixed View
Displays the Result pane at the bottom of the document area.
Horizontal Layout
Switches pane display to the horizontal layout.
All of these commands are duplicated in the Layout toolbar.
Note, that you can change pane alignment with the help of Swap commands in the Comparison menu.