piece of piss.
Take fuel pump fuse out and crank car over - it'll try to start but wont - keep going for about 10 seconds. Remove the fuel cap.
Disconnect the battery
Lift up your boot carpet and you'll see an access hatch cover with 4 bolts holding it on. Remove that being careful not to snap the bolts.
Under that will be the top of the tank with access hatch visible. You need to prise off the two fuel hoses noting which way round they go, and secure them so that they don't slip down the back of the tank. You'll get some fuel gush out, don't worry about that.
Then, undo all 8 (I think) bolts CAREFULLY around the top of the tank - the cover forms part of the fuel pump hanger and basically you remove it as one assembly from the tank, being careful not to bend the float for the fuel gauge.
Remove old pump and solder electrics for the new pump, fit new pump to the hanger and do the reverse of the above.
You could do with a new O ring, unless you want to be a pikey and cut about a centimeter out of the existing one and resealing it (they stretch you see)