An installed hardware of a measuring field device includes at least one transducer reacting during operation to a chemical and/or physical, measured variable of a pourable and/or flowable medium, especially a pourable or flowable bulk good, liquid, gas or the like, as well as a microcomputer communicating during operation with the transducer. The field device is first installed by means of the transducer on, and/or in a process vessel serving for conveying and/or holding pourable and/or flowable media for forming a process measuring point. Thereafter, the microcomputer is booted and a basic software held in a memory provided within the field device for providing, at least in part, basic functionalities of the field device is activated in such a manner that the basic software is executable by means of the microcomputer so that, in the interaction of basic software and hardware installed in the field device, the basic functionalities of the field device are available. Additionally, at least one initial identification parameter set held at least temporarily in the field device and at least approximately identifying the process measuring point is transferred, with application of basic software executed in the microcomputer, to a data processing system superordinated externally of the field device, and at least one upgrade software providing custom functionalities for the field measuring device going beyond the basic functionalities and held in a second memory, is selected from an ensemble of software products, taking into consideration the at least one, initial identification parameter set. A selected upgrade software fitted to the process measuring point is then transferred into a third memory provided within the field measuring device and then activated in such a manner that it is executable by means of the microcomputer, so that, in interaction of upgrade software and hardware installed in the field device, custom functionalities of the field measuring device are available.