It depends on if it's two questions that go hand in hand or really have nothing to do with each other. In the first case, leave it alone. In the second case, try to split it up.
Often, when this happens, you have to be quick. Once there are answers, there's rarely a point in editing the question – in that case, vote to close or flag as not a real question.
But, if there aren't answers yet, I'd propose to make a bold move and edit the question for the OP, so that the post contains only one question. For example, remove all additional unrelated questions. Show the OP how it's done, and if they really want to ask their second (or third, or fourth, …) question, they'll just post another one.
Leave a comment telling them that questions should be reasonably scoped. Point them to the FAQ where it says that. Ask them to post another question, but mention that they should link back to the original post just in case.