get chisel... chisel at the base of the coral to remove it. (you'll only need a 1/4 inch or less of rock layer under the coral) get three tubs of saltwater, keep and cut in one tub, rinse in the second and hold them mounted on the third. Keep them in the third bucket for at least an hour (with flow if you can) so the stuff released from the cut/stress goes off.
As for how to cut, cut a donut shape from the cap, then you can cut the donut into multiple pieces.