With 18mm wrench loose drain plug . Attach some hose 6mm (I think) to control flow of diesel. Perfect would be in some bottle and you can refill filter with that diesel.
Later do not overtight that drain plug. It's by VIDA only 2 Nm. It has 2 o-rings, dont worry.
After you change it, do not start car immediately. Ignition ON and OFF 10-15 times. Let diesel come to high pressure pump.
Use gloves, it will be dirty.
Do not overtight filter cap.
Put some oil on that big o ring