First thing you need to do is to drain the gas tank and put in new gas. Flushing of fuel tank is recommended. Next would be to purge the fuel system and you should be good to go. Replacement of the fuel filter is recommended but don't do it until you have purged the system.
At bottom of fuel tank there is a drain plug. Release the drain plug to drain out the water.
At fuel rail in engine compartment, disconnect it and put hose into a container to collect fuel that comes out. You can either cycle the ignition switch on/off for 2 second intervals to use the fuel pump to purge the lines or manually activate the fuel pump by means of applying battery voltage to it. Once fuel stops coming out of the lines, reinstall fuel lines and you can top up with new gas and try starting.