What tool did you get? This one:
You put the correct size over the line and push it into the fitting. But you can just squeeze the colored clip in to get it off. If you pry on the clip then you can break it and you have to replace the line.
To relieve the pressure find the fuel inertia switch. Passenger side floor up by the dash. Just get on the floor and follow up with your hand untill you see the switch. Pull the connector from it and start the engine. Doing this will not hurt anything in any way.