I dont have a 9th gen manual handy but generally every 30k you should do one drain and flush. I change mine much more often and the difference in shifting is noticeable. Its a very very easy 5 min job that will cost you ~$30.
Buy 3qts of atf from local dealer and a new drain plug crush washer.
Remove drain plug with a 3/8 socket wrench. No socket needed just the square end of the wrench. Wait till fluid stops dripping out. Install new crush washer and plug.
Refill from the top, 3qts or just a little less, with a long funnel. Its the yellow dipstick.
Drive until the car is hot and check the fluid level. I believe HOT is stamped into the dipstick.
Thats it.
Itll help your transmission last longer too. If its been a while you can repeat the same procedure after a quick lap around the block. You dont have to warm the car up. Just cycle the fluid and do a second drain/fill. The fluid breaks down overtime and from heat.