As a general rule European airlines don't do stand-by. The concept just doesn't exist here.

As Mokshu said, if your booking class allows it you can change your reservation to an earlier flight, subject to availability in the same booking class and payment of a change fee if applicable. But if you wanted to do that you should do it now rather than wait until the day as it's far less likely that there will be availability in the same booking class if you leave it until the last minute.

It is highly unlikely that they will just let you hop on an earlier flight for free, the way they would in the USA.