adjustable pressure regulator

[g40tom]

can anyone tell me whats invoved in fitting one of these as i thought my regulator was part of the fuel rail? much appreciated

http://www.ebay.co.uk/itm/VW-POLO-G40-WEBER-ADJUSTABLE-FUEL-PRESSURE-REG-CUP-CAR-GT-SIERRA-COSWORTH-500-/150920736930?pt=UK_CarsParts_Vehicles_CarParts_SM&hash=item232393b0a2