If you typed the values yourself your stuck with the order you typed them in.
If however you transfer them to a table its easy.
I usually have a table for boxes like that to which i add a name column (hiden to the user offcourse) then query that table (order by etc included ) for the values i need for that specific combo box.
If then ever anything changes (need a new value or i made a typo or something) I simply add/delete/update the table and presto changed thru the whole app.
Regardz & GL