For the exterior of the oven use a non-caustic bleach free cleaning spray on the dirty areas. Clean the area with warm soapy water and a sponge or non-abrasive dish cloth and then wipe clean with paper towels.
The best way to clean the inside of the Tread is to burn off any food debris or soot that is left behind. When the oven is over 500˚C it will start self cleaning and any burnt on food will burn off after a period of three hours.