There is round plate on the bottom of the tractor with four bolts in it, this one takes the oil pump apart proper. Wait to do that one after the pump is out. Six nuts around that plate hold the pump to the bottom of the crankcase, but you'll need to undo the crankcase cover on top in order to reach down inside and undo the oil lines connecting the oil pump to the engine.
Now it's time to use a putty knife from above and just scrape the crud out the oil pump hole without wasting a drop of diesel fuel or any other expensive fluids. THEN use a good parts brush with a little fluid and then NEVER flush it as stated since it's now spotless and flushing is no longer needed.
There will be a square tubing drive collar that will fall out when you remove the pump, it is sacrificial in that it is supposed to break apart if there is frozen water in the pump and you try to start it anyway. A friend's hand is nice to hold this part going back together but if you have an upside down bucket and a collection of blocks one guy can manage with some back and forth.
I&T make a decent service manual for a reasonable price if you can still find them - you'll need something along this line eventually if you are asking these kinds of questions.