You cannot adjust the temperature in the oven as its controlled by the thermostat which is factory set.
What is the problem you are having with the oven?
No worries that's fine
Is it the fan assist setting you are having trouble with?
If so is the fan at the back running?
The fan is running. I'm cooking in the middle of the oven.
Ok if the fan is running ok but it isn't cooking as it should then its going to be a faulty thermostat.
As you can only replace it as theres no adjustment on there at all you can do. So when you get this fault its just a case of replacing the thermostat im afraid.