Can someone please tell me the easiest and best way to replace a ignition coil?

I have no spark and I did put new Beru wires and Distributor about 6 months ago.

The coil seems to be designed to slip off the main groove. Is that a correct assumption or do I need to unscrew the two nuts on each side and remove the entire housing and then replace the coil?

There seem to be two main leads on the top and two leads on the housing of the coil - where the coil is attached to the frame (lack of a better word).

Please help?