using DevExpress.Data;
using DevExpress.XtraGrid;
using DevExpress.XtraGrid.Columns;

GridSummaryItem summaryItemMaxFreight;
private void Form1_Load(object sender, System.EventArgs e) {
   // ...
   //  Creating a new summary item and adding it the View's summary item collection.
   summaryItemMaxFreight = gridView1.GroupSummary.Add(SummaryItemType.Max, "Freight", 
     null, String.Empty);
}

private void button1_Click(object sender, System.EventArgs e) {
   GridColumn summaryColumn = gridView1.Columns["Freight"];
   if(summaryColumn.GroupIndex < 0 && gridView1.GroupCount > 0) {
      GridColumn firstGroupingColumn = gridView1.SortInfo[0].Column;
      gridView1.GroupSummarySortInfo.Add(summaryItemMaxFreight, ColumnSortOrder.Ascending, 
        firstGroupingColumn);
   }
}

Imports DevExpress.Data
Imports DevExpress.XtraGrid
Imports DevExpress.XtraGrid.Columns

Dim summaryItemMaxFreight As GridSummaryItem
Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) _
Handles MyBase.Load
    ' ...
    ' Creating a new summary item and adding it the View's summary item collection.
    summaryItemMaxFreight = GridView1.GroupSummary.Add(SummaryItemType.Max, "Freight", _
      Nothing, String.Empty)
End Sub

Private Sub Button1_Click(ByVal sender As Object, ByVal e As System.EventArgs) _
Handles Button1.Click
    Dim summaryColumn As GridColumn = GridView1.Columns("Freight")
    If summaryColumn.GroupIndex < 0 And GridView1.GroupCount > 0 Then
        Dim firstGroupingColumn As GridColumn = GridView1.SortInfo(0).Column
        GridView1.GroupSummarySortInfo.Add(summaryItemMaxFreight, _
          ColumnSortOrder.Ascending, firstGroupingColumn)
    End If
End Sub