There is no simple formula for defining a good specification for a modernized user interface. The special needs of your application, the demands of your marketplace, and the resources of your business will combine to define a practical GUI specification. In this process we recommend that you explore the full range of options available to you, from the small, selective update, to a full reimplementation project.
We recommend that you consider a phased update approach to spread the cost and risk of changing the user interface (UI) over a longer period of time. Remember that ACUCOBOL-GT can support a mix of graphic and character-based screens. The phased approach gives you more time to learn GUI technology in general, and ACUCOBOL-GT GUI support in particular.
Don't forget to develop a test plan. Any significant changes to the UI will require careful testing. You may want some end users to help with testing and evaluation. Be sure to include your test plan in the project schedule and staffing estimates.