Assuming that the vertical scroll bar is displayed, you can position your
mouse over the point between the panes until it becomes parallel lines with
arrows pointing away in both directions. Drag to the top of the scroll bar.
Or use Window | Remove Split.
Asmith,
Move your cursor on the split till it changes in a double horizontal line
with an two arrows, double click or drag to the top of your screen.
Or choose Window menu, remove split.