Carefully open the spring loaded lock by pressing the button (by the green arrow) as you would when raising the whisk out of the mixing bowl.

Remove the black plastic grilled cover that encases the electrics as much as possible to gain access and remove the two screws that retain the curved slotted metal guide. Now the curved guide can be moved aside by again pressing the release button (green arrow). Now it should be possible to remove the black plastic grilled cover.

As all the four rubber mounting bushes have probably failed, the motor can be carefully slid out and put to one side.

Undo the four large motor mounting bolts left in the Kenwood mixer's casing, to release and discard the broken pieces of the old red rubber bushings. These bolts might be a bit hard to undo so use a decent screwdriver (I also used a bit of WD40).

Fit the four new bushes into the holes in the motor mounting flange (as shown in step 1). I soaked my bushes in hot water (80C?) for a few minutes to soften the rubber so they fitted more easily into their holes.

Re-assemble.

You might take this opportunity to replace the machine's five rubber feet (£3 on ebay), as they may be ground flat if it's a very old machine. It might make the machine slightly quieter and allow air to cool the motor better. (Remove old hardened feet remnants with sharp jewellers screwdriver or similar).