Originally the position I applied to was a Manager position. Normally on an interview I don't reveal my salary expectations and wait to hear the best offer, however, on the phone the interviewer pressed hard and I threw out a number that I wasn't totally happy with.

They brought me in, and during the interview they revealed that they were having a hard time filling the position, but also that the position would in fact be a Director position, which could command almost 30% more than the original salary number I had given them. They mentioned my original number fit into the budget and are preparing an offer for me, but I feel as if I have undersold myself, especially because the position is not what I originally thought.

With that, I am definitely going to ask for more, but not sure how to go about doing it, and also how much more should I ask for from my original salary expectation. I feel if I say I want an extra 30% from my original offer they will tell me to get lost. What might be a good way to approach this, and how much more would be reasonable to ask for?