I'd probably remove some water from the system first. (open drain at bottom of radiator with bucket under to catch said liquid) Don't forget to CLOSE the drain! (don't ask me how I know)
I'm not familiar with that tractor... but in general, loosen the fan blades while it's tight, loosen any items holding the fan/alternator/pump belts tight to the pump and remove them.
Loosen/remove bolts to take the pump off. Clean area where pump was (remove any old gasket or sealer)
Carefully affix gasket to your new pump, I usually put two bolts through to help keep it in place. Gently start (only) the two bolts. Don't tighten them down, you want some wiggle room.
Put other bolts in (maybe applying some anti seize on them) finger tighten all down to make sure gasket is intact all the way around. Torque them down and put your front stuff back on, REFILL your radiator and go have fun.