Depends what vintage the car is...
Late 70's/early 80's cars the tank sat on two z shaped metal brackets bolted to the chassis rails
They are the easy ones
Most cars have the fuel tank bolted to wooden boards bolted to the chassis
These require jacking and wedging the axle up to allow the boards to be slid out individually past the leaf springs and u bolts once all the fixings have been removed.
If the boards are rotten or petrol soaked then the simplest removal method is with a jigsaw.....
Simply cut the boards and drop the tank
Then you have the option of either fitting new boards, or a stainless steel tank frame (like the ones I make 😀)
I also make stainless steel replacement fuel tanks for road use, and aluminium tanks, foam filled, for racing
Simon @ SiFab.co.uk