Bad North: Jotunn Edition

When the map with the islands is displayed while playing a campaign, pull the left stick a few times down (). Eventually the detail-screen for your commanders will open. On the right side you can see all the upgrades you can purchase for this commander. If the commander has enough coins for the upgrade, you can buy it. After buying one of the upgrades for one commander, the achievement will unlock.

Hint: You earn coins after every combat (If some of the buildings on the island survived). After winning a fight you have to determine, how many coins each of the commanders will get. After confirming you can not trade the coins between the commanders anymore.