Amsoil will work. I have been doing drain-and-fills using Mobil 1 ATF every 15k. Some will tell you to flush, but I prefer the gradual drain-and-fill method, especially with higher mileage. Yours is not that high mileage, but is pretty old fluid, so that is the way I would go. Drain from the pan. Fill back up through the dipstick with 4 quarts. Easy. Do this 3-4 times with some mileage in between and you will have replaced all of the fluid.