So its leaking at the supply or return line? It should have a quick disconnect on it. The end that hooks to the rail should look like a black bell with a white inner piece. Squeeze the inners together while pushing towards the rail and then pull back and it should come off...install is simple as pushing it back on there until you hear a snap. There are o-rings in the lines that could have gone bad causing the leak
Ok, you might have to get a disconnect tool to remove it. You can buy a set of um at a parts store pretty cheap. Just make sure you have some PB Blaster too, looks like your gonna need it for that rust
It looks like you will need a fuel line disconnect. They are little half circle things that pop on, then push in to release the catches. <$10 at most auto parts stores. I like the metal "scissor" style the best.