How do you change the gear box oil on a TEA20 Massey Ferguson tractor?

To change the gearbox oil on a TEA20 Massey Ferguson tractor, first ensure the tractor is on a level surface and the engine is off. Remove the drain plug located at the bottom of the gearbox to let the old oil drain completely. Once drained, replace the drain plug and refill the gearbox with the appropriate oil through the fill plug until it reaches the recommended level. Finally, check for any leaks and ensure the fill plug is securely closed.