Changing hydro fluid is fairly simple. Your operator's manual has all the information necessary to do the job. Get your filters, the fluid and have at it.
Kubota now recommends waiting until 400/450 hours to change fluid but many, myself included, follow the older instructions and change fluid at 50 hours. One of the filters has a magnetic ring that catches most of the manufacturing bits left in the reservoirs. They definitely recommend a filter change at 50 hours and you'll need some spare fluid for what you lose doing that job.