If I remember correctly the motor solenoid has to be withdrawn either via the boot or under the rear wheel arch liner.

 

I/ve got a 2009 mk3 cleo. Removing the fuel filler need confidence and brut force. After removing 3 screws and twisting off fuel cap, prise up bottom left of unit and pull out. The bit where the central locking come though comes off as a separate bit. Keep pulling! To put the new one in you need it 80 degrees off from horizontal and then twist anticlockwise to correct place. You may need to fiddle piece that connects to central locking first.
I practices in the scrap yards first on the car I got the spare from!

 

For my 2009 model I didn't need to go into boot or wheel arch. As I pulled free the central locking pin pulled out as a separate piece. It pulls off a separate link to the central locking. It falls out of the petrol filler unit and goes back together easy enough