You need to build the Production Center 🏭 to upgrade factories, steamships, and caravans. You can buy this building in your Store, in the Production section.

Tap the Production Center to open a window displaying the list of factories you can improve. These are the characteristics you can upgrade using ingots:
  • The number of shelves you have available for finished goods.
  • Production time.
  • The number of experience points you when completing orders from the Order Board.
  • The number of gold coins you earn when completing orders from the Order Board.
You can't focus on upgrading just one attribute. Instead, you have to gradually improve all the different attributes to unlock the upgrades available at the Production Center.