Remove the rear light on the fuel flap side.
You do this by removing the 2x 10mm plastic nuts from the top and bottom of the side of the light.
Hinge the light away from the car...
...and disconnect the wiring connector.
You can now see the fuel flap solenoid.
Open the boot and look to the right hand interior panel. Remove the Torx20 screw...
...and then pull the interior panel away from the car.
Arrowed below are the 2 fixing bolts.
Use a Torx25 bit to remove these.
Lift the solenoid up and then right to remove it from the car.
Disconnect the electrical connector and it is free.
On refitting, make sure the rod goes back through the hole arrowed below.
Refit the new one in the reverse of removal.