Family-Type Parameters Editor tool in the Editors drop-down of Family Parameters tool-set helps edit parameters of family types in the current family model.
After the button is clicked, it pops up a dialog which allows to edit those parameters.
Each row represents a family type and each column a parameter. If a parameter value field is greyed out, it indicates read-only; otherwise, editable. If a change is made to a field, its color will be changed to yellow.
Only after the OK button is clicked, will all changes (as shown in yellow) be saved back to those affected family types. An information box will report what have been done.
Otherwise, the Cancel button can be simply clicked to dismiss the dialog and discard any changes.