The following sample shows how to remove the first item in the group: Group.Items.RemoveItem Group.Items(0). To remove all items in the collection you can use RemoveAllItems method. The RemoveItem method doesn't remove recursively the item. 

The following removes recursively an item:

Private Sub RemoveItemRec(ByVal g As EXPLORERTREELibCtl.Group, ByVal h As EXPLORERTREELibCtl.HITEM)
    With g.Items
        g.BeginUpdate
        If (.ChildCount(h) > 0) Then
            Dim hChild As HITEM
            hChild = .ItemChild(h)
            While (hChild <> 0)
                Dim hNext As HITEM
                hNext = .NextSiblingItem(hChild)
                RemoveItemRec g, hChild
                hChild = hNext
            Wend
        End If
        .RemoveItem h
        g.EndUpdate
    End With
End Sub