The electronic parking brake caliper should un-bolt similarly to the earlier cable style calipers.
However, the caliper(s) need to be put into basic
setting via a scan tool such as VCDS:
http://ross-tech.com/
Once the parking brake motors have been retracted (calipers
still bolted in place), they can then be removed and the
pistons can be pushed-in (do not have to rotate) to accommodate
the new pads.
Here's a thread with the listed procedure:
http://tech.bentleypublishers.com/thread.jspa?threadID=26955