So i have done the Heater core matrix change and it was not difficult without any mechanical knowledge, however would recommend to have someone to help you as at some stages it looks like you need another pair of hands just for holding a pipe in position or a torch.
Started by removing the glove box and some covers on the passenger side:
Then you will be able to see the heater core and pipes.
After this, remove the media unit and disconnect all cables, all colour coded and different types of connectors, so it will be easy to connect back, but just in case, take a picture for reference.
Remove the foam cover
And remove the fan, few screws holding it.
Remove the sensor in front of the heater matrix, which is blocking the bottom part of it.
Place a tub under and start loosening the pipes.
After that, push the pipe out of the way and slide the heater core out.
Change the core and do everything back in reverse. I have bought new seals and clamps as well for the pipe, don`t need to, but it was just in case. Would at least recommend changing the seals. Was very difficult to alight the pipe and at the same time tighten the screws when putting back together as there was not a lot of room and make sure you put clamps facing the same way as they were due to not blocking the plastic going back in at the bottom of the heater core.
Prior to the task, I completely flushed the coolant and changed the coolant tank, which I bought for 30£ as there was a lot of residue sitting at the bottom of it.
Job done in April.
Any questions I will try to answer when I can.
Thanks and good luck,