Config Field Groups

Dear experts,

I am trying to configure the screen layout of my rental objects and i can work out how it`s working - it`s very different to everything i`ve seen in Financial Accounting before. The IMG guide says that we shouldnt change the field groups, but only add new fields to it. At the same time i want for example to make the fields "land" and "building" in my rental object master data optional or hidden fields????

Please guide me how to work in the screen layout options??

Many thanks in advance!