It should be a 28mm for the front, and a 30mm for the back.

Try to get sockets that don't have a big 'taper' or radius on the end, as the nuts are shallow and thin walled, you need all the engagement you can get. You can grind a bit off the end of the socket to improve that.

Otherwise, it's the same deal as removing the wheels on your M or SS.

I've found the rear is easier to install if the caliper is removed, the caliper bracket is enough of a struggle by itself.