Minecraft wiki entry for Armor_farming, associated text: Once you have got enough emeralds, and once you have got all of your armorer villagers in place you must start to trade. The reason you want multiple of the armorer villagers is because a singular villager can only have a maximum of 10 trades, so to get every single option of armor, you will want multiple villagers with different trades. You will see that immediately there are some iron armor trades and you can trade for as many of those as you want. Once you upgrade the villagers to apprentice you may start to see trades for chainmail armor. Then finally, at expert and master you will see enchanted diamond armor trades. To upgrade a villager simply trade with them enough for the bar at the top to fill all the way up. Once it fills completely the villager will upgrade with new trades. You must be strategic with what you trade, because villagers can only trade 4 times for a certain trade at a time until they restock. Villagers can restock up to two times per game day.