L1R is right and you should accept his answer. Let me be more verbose and you'll see why. Let's start at the beginning of the story.
There was a man of the Pharisees, named Nicodemus, a ruler of the
Jews: the same came to Jesus by night, and said unto him, Rabbi, we
know that thou art a teacher come from God: for no man can do these
miracles that thou doest, except God be with him.
Nicodemus is suggesting there's a disagreement within Jewish leadership: some believe Jesus is the Messiah. Others do not. Nicodemus is among the former, and he gives his reason. He calls Jesus a teacher, and since Jesus is already frustrated with how poorly Jewish leadership understand spiritual things (having fallen far from the truth they once had), He takes advantage of the situation and begins to teach.
Now, either we're missing part of the conversation, or Jesus through the gift of Discernment knew what was bothering Nicodemus. We don't know, but He launches into a discussion that suggests Jewish Leadership had forgotten what it means to return to the Kingdom of God.
Jesus answered and said unto him, Verily, verily, I say unto thee,
Except a man be born again, he cannot see the kingdom of God.
Almost everyone focuses on "born again." Few focus on "cannot see the kingdom of God" other than as a consequence of being born again. Becoming born again was, apparently, not the gist of Nicodemus' confusion — returning or "seeing" the kingdom of God was. We need to keep this in mind, because it relates to your question.
Jesus, however, is a master teacher: and he wanted to make sure he had Nicodemus' complete attention. Baptism was common among the Jews at the time, so Nicodemus would have understood the basic idea, but Jesus' context of tying it to a rebirth was confusing to him — and so it caught his attention.
Nicodemus saith unto him, How can a man be born when he is old? can he
enter the second time into his mother’s womb, and be born?
1 Corinthians 2:14 teaches that the "natural man" cannot receive spiritual things as they must be spiritually discerned. Thus, our "natural state" (the natural state of mortality or the world) is spiritless. Jesus is trying to help Nicodemus understand that true conversion is being reborn to a spiritually-minded person.
Why "reborn?" Because we are first "born" from a spiritual state — where we were before mortality — to a mortal or "natural" state — where we are on this earth. Hense, being "reborn" or "born a second time" combining the best of both worlds: a totally spiritual mortal person. This is the essence of true and total conversion.
Jesus answered, Verily, verily, I say unto thee, Except a man be born
of water and of the Spirit, he cannot enter into the kingdom of
God. That which is born of the flesh is flesh; and that which is
born of the Spirit is spirit. Marvel not that I said unto thee,
Ye must be born again. The wind bloweth where it listeth, and
thou hearest the sound thereof, but canst not tell whence it cometh,
and whither it goeth: so is every one that is born of the Spirit.
Now, that last bit once confused me and I wonder if there isn't a hint of poor translation somewhere, because this concept might be the source of the idea James presents in James 1:5-6. A person not converted is no different than the sea when blown by the wind, having nothing to "interpret" the wind, it simply whips around, not really going anywhere. But add a sail, and suddenly the wind can be harnessed to take us where we want. And were do we want to go? We want to return or "see" the Kingdom of God.
All of this was obviously very confusing to Nicodemus, who had certainly bought into the idea that, as the "Chosen People," they were completely in the right and were assured of God's rewards. Suddenly all the petty behaviors he's been seeing among his fellow leaders are starting to make sense... the "natural man" that must be cleansed by water and the spirit to fully harness the power and blessings of the Spirit to obtain what he wants the most: the kingdom of God. But he hasn't quite put it all together yet.
Nicodemus answered and said unto him, How can these things be?
Jesus answered and said unto him, Art thou a master of Israel, and
knowest not these things? Verily, verily, I say unto thee, We
speak that we do know, and testify that we have seen; and ye receive
not our witness. If I have told you earthly things, and ye
believe not, how shall ye believe, if I tell you of heavenly
things? And no man hath ascended up to heaven, but he that came
down from heaven, even the Son of man which is in heaven. And as
Moses lifted up the serpent in the wilderness, even so must the Son of
man be lifted up: that whosoever believeth in him should not perish,
but have eternal life.
Here's where Jesus nails his point home. Allow me to paraphrase:
I and My disciples have taught and we have testified, but you've not believed Me. I just taught you something you should have understood all along — and you still don't believe Me. You want to ascend to heaven, but if you won't believe earthly things, how can I expect you to believe heavenly things? And there's no one who can teach you these things but me. I want you to keep this in mind, Nicodemus, because just as Moses raised the serpent and all who believed on it were saved from the poison in their bodies, I will be raised up on the cross — and all who believe in Me will be saved from the poison in their souls.
Therefore, to answer your question, it's neither A nor B. "Ascend" is used to underscore the truth that only Jesus has all the answers, and Nicodemus needs to do a better job of paying attention.