How do you replace a thermocouple in canon Oaklley gas cooker?

I have a canon oakley gas cooker and the oven will not stay lit. The oven lights up and stays on when you keep your hand on the knob but the oven goes off as soon as you let go the oven know. Read a few reviews and was advised to replace the thermocouple. Does anyone know how easy/difficult is it to replace thermocouple in Canon Oakley gas cooker?