The list object that holds your business objects must raise some kind of change notification event in order for the grid to know that it needs to refresh itself.
For example, if your list supports IBindingList and your business objects supports some change interface like INotifyPropertyChanged, then the GridGroupingControl should automatically refresh the modified row. But if your business object does not support a changed interface but your list does support IBindingList, then you can explicitly raise the item reset event when you change your object. Here is a little sample.
http://www.syncfusion.com/Support/user/uploads/WindowsApplication16_5dfceef3.zip