Transmission fluid is changed in a similar fashion to engine oil, with a couple of important exceptions. For instance, fluid and filter replacement on a transmission filter often requires removal of the entire transmission pan. Once your vehicle is safely lifted and supported off of the ground for access, a mechanic will remove a drain plug to perform the initial drain procedure. For most transmissions, the mechanic will remove the bolts holding the pan to the transmission, then remove the pan to finish draining the fluid. There is a magnet inside the pan that captures metal debris from the fluid. So, with the pan removed and the fluid drained, the mechanic will manually clean off the magnet.
Next, the filter - typically wide and thin, as opposed to can-shaped like an oil filter - is removed and replaced. The pan is reinstalled with a fresh gasket, and the transmission is refilled with fluid from either the dipstick tube or an access hole on top of the transmission, requiring a special pressure pump and adapter (an increasing element of late-model vehicles).