You can't turn off the split screen but you can minimize it by clicking on the small inverted triangle symbol on the horizontal split bar. You can also manually drag the split bar to adjust the size of the split screen.
You can get a lot of info at the bottom split screen. E.g. you can get keyword help on any TBASIC command. Simply select a keyword and press F1 key and the syntax is displayed below which is very useful when you need to enter a command but don't remember exactly the order of the arguments.
