It is easier than most. If you have ever done any disk brakes, this will be a cinch.
BMW uses a silicone grease on the backs of the brake pads rather than teflon shims or gooey stuff to quiet the brakes. Any on-line vendor that sells brake parts for BMWs will sell you that grease.
Before you buy new pads, pull off a wheel and have a look to see how thick the pads are, and to see what kind of shape your rotors are in. Original BMW pads are not only very dirty, they are also pretty hard on rotors.
I recently bought a 325iT and the PO put slotted rotors and stainless braided lines on it. The rotors buzz a little as slotted rotors tend to do, but they look and work absolutely great. I wish I knew where he got them. I have three other 3-series with Mexican-made Brembo rotors and AAXIS pads on them. They work great, and keep the wheels clean, but the rotors rust like crazy when they get wet.