A controller for a bathing unit system comprising a memory unit for storing program instructions, an interface for establishing a communication link with an external memory medium and a processing unit. The controller is operative for controlling a set of bathing unit components at least in part on the basis of the program instructions stored in the memory unit. The external memory medium stores update information associated with the program instructions and relevancy information indicative of a characteristic of the update information. The processing unit is operative for detecting the presence of an external memory medium at the interface, accessing the relevancy information stored in the memory medium, processing the relevancy information and causing the program instructions to be updated on the basis of the update information.