The new coil leads are terminated with the crimp inserts that snap into the plastic plug. They usually have a barb on them that locks the crimp into the plug. It may be possible to remove the existing wire from the plug by pressing down on the barb so that it can be pulled out of the plug, maybe by using a scalpel or a very small screwdriver. If you can get the old wires out of the plug without damaging the moulding the new inserts should just push in and snap into place. Failing that, you'll just have to cut the old wires off and splice them to the new coil by soldering or use a butt splice crimp.