Overbuilding

Overbuilding happens through the Build action itself — discarding a valid card and paying the new tile's full cost, same as any Build — but lets you replace an already-placed Industry tile with a higher-level tile of the same industry type instead of using an empty space. You may always overbuild your own tiles this way. Any coal, iron or beer on the replaced tile goes back to the General Supply, and the replaced tile goes back to the box: it scores nothing, and its owner loses no income or VP.