Changing Transaxle fluid

Hi guys, I have a 2002 or 2003 38" deck joystick model ZTR (BZE1538) & live in Western PA so I store it in outdoor shed over the winters & have never changed the Hydro fluid before. I am concerned with possible condensation contaminating the Tranaxle fgluid but couldn't find any info on this project. Is there any info out there on this? I am very capable of repair & maint. on any vehicle & wouldn't mind doing it myself with some proceedure instructions or is there some reasons that this is Dealer only project?