When should I ask for an update?

After many interviews with the same company but speaking with different people, I have no idea if they're moving me up in chain as a potential candidate or just keep talking to me for then at the end I will be rejected. I think that when a company is moving you up with other people within their company to interview, it's a good sign. But is it enjoyable to be unsure about each interview? No, absolutely not. The act of not knowing really doesn't help ease the stress through each interview. But how can one approach them for a good or affirmative sign to get good news? How can you ask them without being "pushy" or "rude"?