Buy Toyota premixed red coolant 4 Ltr. I paid about 2350.- last year iirc. Get it changed from them, much better. They will clean out the system as well, could be loads of chit inside it. Watch them do it and then you can do it yourself later on. Just saying because auto cars have a pipe that goes from gearbox to the radiator, ensuring that the atf fluid doesn't get too hot. Just watch and learn;)
Otherwise, put car on jackstands or visit nearby Car wash, raise the car, under the radiator should be a plastic screw, use flathead screwdriver and open it, squeeze radiator hoses and get it all out.
