The Acropolis, Athens

There is an elevator but as I understand it, its use is fairly well regulated and you must have proof of disability.
I frankly found seeing the Acropolis from afar more emotionally satisfying than seeing it up close, but I would probably tough it out and take it easy the next day.

My wife has knee pain after walking up or down a flight of stairs. She was surprised to find the Acropolis wasn't too hard on her. It's mostly a gradual uphill with a few steps here and there as I recall. But your problem is with uphill walking so I can't guess how it would affect you. I'd say there is a lot to see up there, though you can no longer go right into the ruins as in the past. The view from the top is also very good. You might give it a try and prepare to descend if necessary. The sculpture is all in the Acropolis Museum, with good elevators.

My understanding about the existing elevator is the same as the previous poster's, it's small and they're fussy about who's "disabled" enough to use it. But you could try. It's on the north side, but I don't know specifically how to get to it.

EDIT -- I just found this website about a new elevator that opened last year, seems to be bigger and more reliable, and also mention of new routes for disabled visitors. You might want to look at this and do some googling to see what your options might be. My own info is several years old.

The walk is not steep at all and there's no reason to rush, there are a few things to see on the way. The last bit is stairs, but maybe one flight. The top is flat. There are a few streets in the central Athens that are on an incline.

You could take a taxi up to the Acropolis entrance. That will eliminate a lot of the walking. As noted there are steps up into the Acropolis but not very many Just take it slow. I too have a bad knee. The Acropolis experience is worth it.
Get to the acropolis just before opening. You will beat the tour bus crowds and have about an hour with just a few hundred other people versus a few thousand later on. It is also cooler in the early morning.

The walk up was not nearly as difficult as we expected. Give it a try!

I'd suggest you give it a try. It's not that hard.

You are in Athens, I feel like you must go up there!! As others said, it is not a very difficult walk. And you can rest along the way. Maybe buy a walking stick to help a little.