Well, if your change of direction is a result of what you have done so far- i.e. you have hit upon something more interesting, or your initial theory was partially/totally wrong you could mention it. You'll probably get people asking the "obvious" questions that arise from your presentation anyway.
Have you got enough data for your presentation? If you have enough time then do it, if you are already short on time then leave it out because it can become very confusing if you try to squeeze it in in the end.