To replace a fuel tank, a technician will need to perform a series of steps that are common with most vehicles.
For instance, your vehicle must be safely raised and supported to access the tank underneath. Power to the fuel pump is disconnected and the fuel system is depressurized before the tank is drained of fuel. The filler neck hose is detached from the vehicle body. The tank is supported, the straps that secure it in place are unbolted, the tank is lowered a bit. The fuel lines, vent lines, and electrical wires are disconnected. Then the tank is removed from the vehicle and its components (i.e. the fuel pump) are extracted and installed on the new tank. Installation of a new tank into the vehicle involves essentially the same procedure in reverse order.
While these steps are fairly common when replacing a fuel tank, additional steps might also be necessary, depending on your specific vehicle make and model. For instance, suspension components, drive shaft, and other parts might need to be removed for access. And great care must be taken when replacing a fuel tank in a vehicle because fuel vapors present an explosion hazard.