Officer's Patent

[Hunkie]

From battle_akademy.lua:
Peasant > Footman/Bowman/Priest/Pirate/Robber
Footman > Guardman/Witch-Hunter
Guardman > Knight/Horseman/Paladin
Priest > Inquisitor/Witch-Hunter
Archmage > Necromancer/Demonologist/Rune-Mage
Pirate > Sea-Dog/Ghost-Pirate
Dwarf > Cannoneer/Foreman
Orc > Veteran-Orc/Orc-Tracker
Veteran-Orc > Ogre/Ogre-Chieftain/Troll

I've also found this from the script:

Hero_unit_count_tc_new = math.floor ((tc_army_leadership_1*Hero_unit_count_tc_old)/tc_army_leadership_2)

I think it can be translated to simple English like this:
NewUnit_Number = Round-down ( OldUnit_Leadership * OldUnit_Count / NewUnit_Leadership )

Priest's Leadership = 50/each
Inquisitor's Leadership = 100/each
You have 20 Priests.
When upgrading to Inquisitor, you'll get 50 * 20 / 100 = 10 Inquisitors.

Footman's Leadership = 35/each
Guardman's Leadership = 50/each
You have 25 Footman.
When upgrading to Guardman, you'll get 35 * 25 / 50 = 17.5 = 17 Guardmen.