When I first adopted Luna, I was living in a fourth floor apartment. Our only access to the fourth floor was outdoor, concrete, open-backed stairs. Since they were outdoor, so was on a leash, so I just walked her on a close leash so that she would take the stairs slowly, both up and down. She was apprehensive at first, but within a couple of days, it became second nature, and all was well.
Best of luck to you as you move forward with the adoption!