Unplug the wiring and then unbolt the fuel rial and remove the fuel lines and pull them out. A bit of fuel will spill out when disconnected. They just sit there held in by the fuel rail. You might have to remove the manifold if it is in the way. You will need to get the same size that is in there all ready. If you have aftermarket ones and you put stock ones back in without a tune it will run even more crap. Make sure the plugs for the wiring is the same. If they are aftermarket they could of been cut and modified.
It's not a hard job but if you don't know much about engines I would give it to someone to fix.