To fit simply pull out your existing coupler from its NEM coupling box and push the new coupler into the empty housing. Do the same again for your rolling stock, and also fit a Dapol uncoupling magnet between the rails at ballast level.
This system makes uncoupling over magnets very easy, and also allows the pushing of the uncoupled train (from over the magnet) to anywhere on your layout without it re-coupling up. For the first time hands free shunting becomes a reality in British N gauge. old code NSPARE7A