You are asking way too early. Ask again 1-2 days before the flight to get a much better view of the situation.

The chance of a free upgrade to C is slim. Most likely there will be some pax ahead of you in the line for upgrades.

However, if the flight is oversold and you volunteer for VDB (volunteer to take the next flight) but your seat is not needed at the end of the day and your seat has already been allocated, your chances of a free upgrade to C are pretty good.

The compensation to take a flight the next day is EUR 600.