It all depends on whether the scew heads are flat, or have slots for a screwdriver.
If no slots , then you are going to have to access the heater from the rear of the outer rear cover of the oven.
If the screws can be undone from inside, then simply unscrew them, and pull the element out towards you.
Hope this helps.

First remove 2screws/nuts in the oven that holds back plate
remove 4screws that holds oven in kitchen cabnet
pull oven out
remove back cover
remove wire from old element element is held by nuts remove nuts and putt every thing back together
element you need is on link here element code AB20
http://cookerandovenelement.co.uk/bellingfanovenelement.html