First of all, are you sure it is the elements and not the controler? To test the elements, lift theplate out of the worktop, change the 2 wires from a good element to that element. put the plate back in it is home and use the good elements touchtronic button to turn on the element. I am willing to wager that it is the control unit and not the elements.
Remove hotplate and oven control knobs. Under the 2nd and 5th knobs is an extra screw which holds on the front cover. Unscrew these and free the cover then access is gained to the screws (2 on each edge) which removes the plate to which the regulators are fixed.Remove the faulty regulator by unscrewing it from the plate,(2 screws) It is an easy job then to install the new part taking care to put the correct wires on the correct terminals. Reassemble, job done!