Indesit washer/dryer model WD12UK?

I need to replace the sensor on the dryer and I am not sure how to do this. I think this is the problem since the machine seems to be working in all other ways but yesterday it set the trip off.When I put the trip switch back up it continued to work until the end of the cycle but even though I had had the tumble dryer on for over a hundred minutes the load was still wet and cold.