* Disconnect the battery's negative terminal. This is a crucial safety precaution to prevent sparks near fuel.
* Drain the fuel tank. This is also a crucial safety precaution.
* Lower the fuel tank. This usually involves removing various components underneath the car, like exhaust components and possibly the fuel lines.
Because of the complexity and safety concerns involved, this is generally a job best left to a qualified mechanic. Trying to access it yourself without the proper experience and tools could be dangerous and potentially lead to damage.