Hi,
I could'nt find a guide for doing this and its very easy on an SPI mini so though I would put up some pics for anyone else who might not know how to get the job done...
firstly I disconnected the hose from the heater control valve in the engine bay, to stop the coolant possibly sucking more through when I take the hoses off the matrix inside the car..
there are two hoses going through the bulk head, I was happy just disconnecting one to relieve pressure
Then inside the car, two screws hold the matrix into the left hand side of the heater, four screws and 2 jubilee clips hold the two coolant pipes in place ( I found I couldnt get enough grip on the pipes to just pull them off once the jubilees were undone, so undid the flanges that hold them to the matrix and gently prized them off with a flat head screwdriver)
once you have taken the pipes off, the matrix just slides out.
Putting back is just a reversal, though watch out for the foam in the matrix, it will roll up, i've read using a card template on the matrix while pushing it in stops it rolling up.
The reason I had my matrix out was that I was'nt getting any heat except under load, doing about 50mph... so since the pipes were hot even on idle, I figured the matrix was blocked, once I had the matrix out I took it inside and blasted the tap through it both ways...when I put the matrix back in and reattached pipes in the footwell, I filled up the pipe from the valve end in the engine bay with coolant and blew it through the matrix, filling it up and since the heater is now working on idle, it must have been an air block :)