You can replace one group with another by selecting a group and then choosing a different group name in the Type Selector. Revit automatically replaces the group.
When you swap an instance of a group type for an instance of a different group type, Revit attempts to replace any attached detail groups from the old group instance with attached detail groups of the same name from the new group instance. For elements in attached detail groups that were not replaced, and for all other elements that depend on elements in the swapped group instance, Revit attempts to find references within the new group instance. If new references cannot be found for these dependent elements, Revit posts a warning to indicate which dependent elements it could not find references for. In addition, the origin of the new group is placed at the position of the first group. For more information on group origins, see Specifying the Position of a Group by its Origin.