From summer 2007, it has no longer been necessary or possible to decline grades.
So, you have accepted the grade. But since that was 2007, it is still in the marks are still in the bank, whereas before by accepting the certificate you have withdrawn the marks. But at the moment you still have the marks.
Resitting means adding another mark of the same unit into the bank, and letting the best mark count. So you will have the best mark count.