How does backup exec 2012 reuse disk space once backups have expired?

Hi Folks

As the post says, im trying to find out how backup exec 2012 reuse disk space once backups have expired?

I have almost run out of room on my server disks. i have set expiry dates for retention which tick over tonight at 12am. Does backup exec delete the old backups once the expiry date has passed?

Cheers