You need to purchase an Operator's Manual from an Ingersoll dealer if you do not have one that is specific to the serial number of your tractor.
You should go to the Ingersoll website and print out the correct parts manual for the serial number of your tractor. It's free.
You should understand up front that Case no longer supports these tractors because they sold that division 27 years ago to Ingersoll.
You need to drain the hydraulic system and refill it with 20W50 motor oil. Then change the engine oil and refill with straight 30W. You can use either of those oils in the trans-axle when you change that oil out.
What else do you need to know?