Starting from level 15, the Trade Company allows you to upgrade your factories and worker houses.

Here’s how you can do it:

- Tap on any building you wish to upgrade.

- Tap on the blue star with a number.

- If you have enough materials, tap Build.

All upgrades are shown at the top of the menu. The upgrades are unlocked strictly in that order, so you can only enable them one by one. You can also scroll the upgrades menu to the left. Unlocked upgrades have a green check mark.

To learn more about an upgrade, tap the question mark "?" next to it. 

To see all the upgrades currently unlocked in a building, tap the big question mark “?” in the top left corner of the screen. 

Attention! If you sell an upgraded building, all the upgrades will be lost with it.