Just beneath the cathode assembly is plate protecting the filament terminals. Carefully unscrew few turns the two Phillips screws holding the plate, with out completely removing the screws. The plate should automatically slip down revealing behind it the two terminal posts for the cathode. Now tighten the Phillips screws back with the plate down. Frontal view of the cathode.
Wehnelt window is visible at the center top.
Using a metric hex wrench unscrew the two hex heads holding the high voltage wires to the bottom legs of the cathode assembly. These are captured screws and will NOT come out of the terminals. Remove the wires away from the legs of the cathode. Now with the other hand unscrew the hex heads present at the bottom corners of the cathode assembly. Place the cathode assembly with the hex heads facing up on a clean Kimwipes sheet.