There are 2 ways you can calculate the new total after removing an item from your "order".
1st you deduct the value you've removed from the total
2nd you add all the remaining values to get the new total.
I'm guessing you went for both ways at the same time.
Since you are declaring Sum for each record removed, it will be 0. Then from 0 you deduct all the prices currently found in your DGV2 (
For I = 0 to DGV2.Rows.Count - 1 )
Sum -= DGV2.Rows(I).Cells(5).Value to
Sum += DGV2.Rows(I).Cells(5).Value and you should be fine.