Rangemaster 110 - How to replace electric hob plate?

Hi I've got a 12yr old Rangemaster 110 all electric cooker that's tripping due to a faulty back left 1800mm hob plate and thermostate failing. I've no idea how to get the hob out? I recently replaced the oven element and I've checked the wiring at the back but can't see how to get the top plate that holds all 4 rings in place off? Please help!!

JohnD
January 2010