Merry Christmas to you all up there

Have been enjoying my travels in my van but as its our summer down here I thought I would do some maintenance on the heating system or our cold winters. I notice a coolant leak on the passenger side floor and it has been running onto the ECU unit, which is not ideal.
My question is how do I get the heater core out. I searched on here but I could not find anything.
Thank you in advanced
Cheers