How can i change the position of an item in the list box in c#.net with asp.net2.0?

iam preparing a listbox it contains some items , and it has two buttons ( up button and down button), when i pressed down button item was changing its position from up to down , but when iam pressing the up button it is not moving ????..this is my prob what to do pls make me clear.......... iam doing it in c#.net with asp.net2.0

How can i change the position of an item in the list box in c#.net with asp.net2.0?
delete and start from the beginning