Carefully lift the arm on the side of the processor and lift it up to release the tray mechanism.

Remove the old processor carefully by the edges (I had on a pair of latex gloves just as an extra precaution)

Replace the new processor, taking care to line up the notches, which should go towards the hinge on the CPU cover. The pink arrows in the second image show the placement of the notches.

Carefully lower the cover and replace the arm. You will feel a bit of spring tension, but it should come down with relative ease.