Petrol or diesel is the main question. Petrol is usually a banjo union at either end with different threads to stop you fitting the wrong way round. If diesel its more fiddly but still simple. You need to unscrew the centre nut on the housing unit and lower the filter unit into a container(only to catch fuel). Discard the filter, and "O" RING at head of bolt and also in filter head(where filter would fit into) and fit new items which should be supplied. dont worry of extra "O" rings as they are for different applications. Fit filter to base and mate with top housing. Gently screw in bolt so as to not damage thread and nip 1/4 turn to tighten. Hand prime with pump on filter assembly bleeding as required.
Alan
May 2008