When should I change the transmission fluid on my Astra?

I own an Astra J with the 1.4 petrol engine with an auto transmission. The car has covered 65k. I know that every automatic transmission, sooner or later, needs a transmission fluid change. My local garage says the Astra has a permanent fluid and that - if I really want to change it - can be changed in part. Can you please tell me if this is correct? Does the auto box need a fluid change? And, if so, when or at what mileage?
They don't have the proper equipment. Just draining leaves 2/3 of the fluid in the convertor. Take it to a member of www.fedauto.co.uk and ask for the fluid to be changed by the dialysis method. New fluid is pumped in at precisely the right temperature and pressure while the old fluid is pumped out. Like a blood transfusion.
Answered by Honest John on

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