Which set do have? The plastic or the metal ones?
There's actually two sizes that you'll need to use and I don't remember off the top of my head which ones they were. Doesn't really matter though... You'll see the portion of the fuel line that flares out to a larger diameter at the connection point. Use the size that fits best around that flared end.
The way that you use these thing:
There's a spring lock inside the connection. Install the tool the apply a considerable amount of pressure to get the tool up underneath the spring to release it. Then pull the two pieces apart.
It's kind of a pain in the ass if you've never done it before. You have to push on the tool as you pull the two portions of the fuel line apart.