I asked about changing my coolant last year, and finally decided to do it, thought I'd share my experience.
After removing the overflow reservoir, and dumping the coolant out of it, I noticed some tan precipitate on the bottom of it. It washed out easy enough but, I decided to buy demineralized water and flush the entire system. I ended up flushing it three times. I was originally thinking I would just drain it and add the new coolant since the Tractor only has 200 hours and is just over 3 years. I chose not to take off any hoses and just use the drain at the bottom of the radiator. As a result, only 4 of the approximate 6 plus quarts of coolant came out each time I drained it.
As noted in the earlier posts, when I filled it up with the pre mix coolant, it was diluted by the 2 plus quarts of demineralized water that was left over from flushing. I ended up having to drain about 5 cups (done over 3 intervals) of coolant and add full strength coolant to get it to the proper freeze / boil over protection level.