The real question is, what are you taking your key press from ? If it's a PC keyboard you'll need to use KEYIN and check the 'keyvalue' returned. If it's some serial based terminal you would use SERIN, and you'll probably have to do some experimenting to find what byte value(s) the terminal sends for the arrow key as I'm not sure there is any standard.
There's no simple answer to your question because it's not clear exactly in what context you mean.