Find the exact model number o fth eovern and see what the spare looks like. Do a Google search for "lamona oven spares" and look for the specific part you need.
TURN OFF THE OVEN AT THE ISOLATOR SWITCH
You could also take out the relevant fuse from the fusebox and put it in your pocket.
Get a couple of sheets of paper and a pen to make sketches of what screws, wires and sundry bits go whewre
DON'T RELY ON MEMORY
You'll probably need to take the back off to get at the fan motor and mounting screws.
You will probably need to remove the fan blades from the motor spindle to withdraw the motor (Check photos of the spare). If so, you will, very likely, need to remove the back (?) of the oven liner that covers the fan.
Check the spoare against what you see before you do anything more. If it looks correct proceed.
Disconnect the fan cables (Making notes). Unscrew and remove the old one - make sure any insulation under or around the fan doesn't get damaged or displaced.
Replace the motor, replace the cables, replace the fan blades.
Check the fan rotates OK
Replace all covers (just 'nip up' the screws - don't overtighten)
Check for missing bits. Check again the fan rotates OK
Power up and checck for correct operation.
Make tea.
X, March 2015