Yes the 2 'yellow' pipes are the top of the matrix, and are these are what the water pipes in the engine bay are connected to.

From memory (it was about 3 yrs ago I did one), 2 x 13mm bolts, the whole heater will be loose for you to wiggle the heater box down (its massive!) and the matrix will slide out! There are also some cables that contol the direction flap on the passengr side of the heater that will need disconnecting as well (1 self tapper)