Hello and Welcome to justanswer...
The first thing you need to do is go under the bonnet - locate the two hoses going into the bulkhead (heater ) and disconnect them.
Then , working inside the car,.. from both sides of the central unit... remove the plastic trim from both sides - then you will see a black box ..
(You may also have to remove the central plastic sections that surround the gear lever and handbrake to get good access - not always necessary but some find it easier to do that )
If you look and feel around the lip of the box you will see /' feel some 8mm screws - you need to remove these all around... ( can be a bit tricky because of access but can be done -- ) then the bottom half of the black housing will come away --
Then you will see the heater matrix and you can extract it --
Fitting a new matrix is an exact reversal - remembering to refill the cooling system.
I Sincerely XXXXX XXXXX have helped you - Please ask me if you need more help...
Kind Rgds,.... MIKE
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