This tells us couple of things.
I already mentioned, that one way of rising in the ranks was military service. This could been individual effort, or those who happened to born into a group that had freedom, such as the Székelys or the Hajdús, well they got a headstart here.
Another way was the Church. Becoming a cleric meant advantages for the whole family, this could help relatives to move forward as well.
Third the burghers, in civitas' (civiti???) - in the cities - most of them could advance within their profession, in their guilds, and became patrician eventually, or hold some other office of their commune, or again both the Church and military was open to them.
Serf could move to a city and became a burgher. Except they were tied to the land by law, and it was forbidden for them to move anywhere, even if it was the land of another noble. Essentially this law was enacted to prohibit competition between nobles. Still serfs tried to move time to time. I'm not sure how exactly was on the Hungary, but from universal history it is known that if a serf spent X amount of time in a city, he became free.
The example of Bakócz Bálint (the elder brother of the future cardinal) shows that even an oppidum offered opportunities, if one knew people and had at least some talent. The Church had no need for dumb people, and they demanded diligence too.
Those living in villages were probably in the worst situation. Their only way probably was military service. Perhaps they could be some kind of a minor office-holder on the personal holding of a noble, like a stablemaster or whatever chief hunter.