Decent quality spanners are a must! The is a larger nut welded to the bottom of the fuel filter you can hold iirc its a 19mm. I have just done this, and it was such a pain, but hopefully this will help. When undoing the top bolt, I held the bottom with a spanner. Use plenty of penetrating fluid like Plus-gas not wd40. When undoing the lower nut, as it was just me I did it from underneath, holding the larger nut with a spanner on my left, and the smaller union nut on the right behind the engine with my right. Then its just brute force and ignorance. Undo your petrol cap before you start though to release the pressure, otherwise fuel pisses everywhere.