In general, you will need to raise the 525 onto jackstands (or a lift if you have one), remove the transmission fluid drain plug, catch the fliud into a wide container, remove the transmission fluid fill plug (above the pan and to the driver's side), and let drain. At this point, you should consider unbolting the trans sump pan to replace the trans fluid filter. If not, reinstall the drain plug an refill via a pump the transmission sump via the fill hole. That's about it. Check www.bimmerfest.com for lots written on this subject.