1. Turn the printer off and unplug it from the wall
  2. Remove the three screws and spacers above the heat block.

  3. Pull the assembly down and remove the circular spacer and heatsink.

  4. Remove the tubes and replace them.

  5. Put the heatsink and spacer back on the tubes.  Remember that the heatsink flat side faces down on the brown insulator.  The face of the heatsink that has the raised ring faces up toward the spacer.  See picture in step 3.

  6. Put the three screws and the spacers back in.  Each of the spacers should have a washer attached to the bottom end of them.  See picture in step 1.  Attach the washers to the spacers with a dot of super glue if they've come off.