County of Fortune how to change production: demolish the building and replace it. Hover the building in the settlement's Buildings tab, use the "-" symbol, and all the resources that went into it come back — so changing production costs you time rather than materials.
County of Fortune how to change production: the steps
Open the settlement, go to the Buildings tab, hover the building you want to replace and click the "-" symbol. The slot is then free and you can build the replacement in it.
Because the industry you picked when founding the settlement is simply the first building of that settlement, you are free to turn a farm into a logging camp or into a workshop. Building slots covers how many buildings you have to work with while you swap.
When changing production is the recovery plan
This is the intended way to recover from a dead end. When a region cannot meet a need, delete the buildings that create the demand you cannot cover, build three different foods in three different settlements, and then add wood, chests, sheep and tunics — the standard route back to a working peasant economy. Buildings are easy to destroy at any time and you get back all the resources, so you can replace them and move on as your population's needs evolve.
What you can also change
You can change who runs a settlement instead of what it builds: swapping mayors between settlements is free, and demolishing the affected buildings and putting different ones in their place is always an option. Choosing a mayor covers the swap itself, and building slots covers how many buildings you have to work with in the first place.
What you cannot do is delete the settlement itself — only the individual buildings inside it. Deleting a settlement explains what that leaves you with.