Hi and welcome.
It is most likely that you have to have a condensing boiler installed. These can be any type of boiler*** (combi, system, utility). The condensing part refers to the re-heating of the flue gases. Due to this, an extra pipe will need to be installed to drain the condensate (slightly acidic water).
This is the major change of pipework.
Referring to the four pipes mentioned one side will be water and the other the radiators (at least this is what to expect). Each pair of those pipes should have a pump and a zone valve (silver box on the flow pipe). You can think of these zone valves as water switches. If the heating is calling for heat the heating zone valve will open the water circuit (and close when the heating's satisfied).
Finally, you have the oil pipe.
Most likely, the pipework will need to be altered as all boilers have their flow and return connections in different places. The alterations will generally be fairly minimal though. The oil line will probably have to be moved as well.
Building regulations say that when a new boiler is installed you have to have: condensing boiler*, pump, room thermostat, programmer, thermostatic radiator valves (all rooms except where room stat is), a separate fused spur (usually 5 amp), a fire valve correctly fitted and there are a few other matters e.g. the flue termination.
*in most cases.
The installer might deem it more sensible to change your pipework around so you only have two pipes (one flow and one return) coming from the boiler. The flow will have the pump on it, then a tee in the pipe and after this a zone valve for the hot water and a zone valve for the central heating. This means that instead of running two pumps (if that's your set up at the moment) you'd only need to run one. And the second one you can keep (in storage) in case the first one fails.
You've not asked for prices and I don't know the size of your house, but generally your looking at a bill for around £2,500 to £3,000 and 3-4 man days. I tend to work with someone else for one day and finish off on my own the next day on my installations. This means you're without central heating for that time but the immersion heater in the hot water cylinder will still function so you have hot water all the time.
It's important that you choose someone belonging to a competent persons scheme (usually OFTEC) as installing a new boiler is notifiable and normally the boiler's warranty is only valid when it's installed by an OFTEC Technician.
*** Edit ... when I say any type of boiler I don't mean any type of boiler is suitable for your house. I doubt a combi boiler is suitable for instance. More information is needed (number of rooms/radiators their size, number of bathrooms, baths, showers, etc.)
