You need a small flat screw driver bent at 90o As shown below

Adjacent to the ON/OFF knob is a small hole. Inserts the screw driver into this hole and with careful leverage release the catch which locates the knob and lift off.

IMPORTANT: Treat the switch knob with care when releasing the catch as it can be very easily damaged! The above tip is meant only for engineers/machenics/elctricians who are not familiar with the access procedure. In the interest of personal safety, we do not recommend general public to replace either the switch or mains lead without specialist knowledge.

CABLE FITTING GUIDE:
Replacement of mains cable must only be fitted by a suitably trained person.
1. Make sure your hoover is unplugged from the electric mains supply socket.
2. Before you remove old cable, make a note how wires are connected to switch and connector block.
3. Before inserting cable into the entry hole, fold back NEGATIVE lead with bare end. This allows the insertion into hole of the POSITIVE lead with connector already fitted. The NEGATIVE lead can then follow through and the cable itself.