You can upgrade all Appliances (stations and sub-stations) by collecting enough Appliance Cards and by spending Coins and Blueprints.
Blueprints can be earned by completing the orders in Booster Boat in the Dock.
Winning challenges in Chef Masters will earn you Chef Box which contains Appliance Cards as rewards. Appliance Cards can be collected from the free Daily Chef Box as well. The other option is to purchase a Chef Box using Cash and collecting the Appliance Cards from the Box.