how do i fit an element to my oven model zanussi zuf270w?

hi can you tell me how to fit an element to my double oven .its the main bottom oven thats gone we bought the oven second hand and we were told that the thermistat had gone on it .we bought a thermistat but that didnt work so we got an. element where do i find the element and how do i put a new one in .the oven does not heat up at all if this does not work i dont know what to do or what to look for if you have any idea what else we can do we woud be very grateful .also i dont have a users manual for it can any one tell me where i can get one .as it has a timer on it and we dont know how to use it .we would be gratefull for any advice .thakue sheila