Retraining a level - skill ranks and hit points

[LucyG92]

When a character retrains a level in one class to another, what happens to their skill ranks and HP?

I'm assuming they remove/add the difference in ranks, between the two classes? Players aren't expected to know what skills they put ranks into when they took that level, are they?

I can see re-rolling the new level's die for hit points, but again, the question of how many hit points were gained at the level comes up, so I'm stuck on what to do with that.

[dragonhunterq]

Simplest solution:
Let the player choose the skill ranks to lose/gain - as long as the max ranks limit is observed no harm no foul.

For HP go with +/-1hp for each die step changed (difference between the average roll)

[James Risner]

+1 dragonhunterq method I likes