You don't take the fan off. If it's a reversible type you push the blades towards the center hub and turn 1/4 turn until they pop back out. That way the leading edge of the fan is now pulling air from the rad side of the fan as opposed to the engine side of the fan.
If cleaning doesn't help then I'd open the rad cap... CAREFULLY and look in there for bubbles while it's running and check for circulation or other evidence of crap. It might be that the cooling system needs to be drained and thoroughly cleaned. I use a fast flush type of acid product available at NAPA and other such places...
The machine should cool itself fine if everything else is in proper working order. IT may be marginal... but it should cool.
How hot is it running anyhow? Is this a Cummins engine or the old big bore Case engine?