You need to remove the holding screws on the bracket at the back of the grill securing the grill to the frame. The whole grill assemble will then pull forward out of the fixings. This is a bit fiddly but it does come out, be careful not to damage the back of the elements / wires when you pull the tray free from the oven. To reassemble you will need to remove the back panel to connect the the wires back onto the elements. (isolate electric supply before attemting any repairs)
Glen, November 2007