As you are starting from BRU, there is only one Z-fare and there is nothing in the conditions that would stand against upgrading to F. So call the SEN hotline asap, perhaps there is space in O-Class for an upgrade, if not ask the agent to put you on the waitlist and you'll receive an email as soon as your seat in F has been confirmed. Availability will be checked by the computer system about every 4 hours.
So have a nice flight!