Take your ignition key and insert it into the seat lock located on the left hand side of the bike, about 1/2 way down, in front of the pannier (side-bag). Turn the key to release the rear portion of the seat first and lift it up and rearward to release the front end of the seat from the tang at the rear of the gas tank.
Sometimes the key may be hard to turn. If that is the case, then push down hard on the rear part of the seat as you turn the key (it should turn about 1/4 turn).
Your gas leak is probably one of the rubber gas lines located under the left hand side of the tank. You'll need to remove the gas flow knob with a phillips head screwdriver leaving just the stalk. CAREFULLY lift the tank up!!! There are hoses and your gas gage wiring attached to the underside of the tank that you should remove gently. Be sure to turn the gas flow knob to the OFF position when removing the tank or else you'll be wearing all that gasoline. I normally gently lift the tank from the rear and slide something underneath that end to hold it up while I remove the fuel hoses, vacuum hoses, and wiring.