You're talking about the cable that goes from the gas to the throttle body?
You don't really adjust it. The cable is a specific length, if you're curious if its operating properly, push the pedal to the floor with something that will hold it there, or have someone help.
Then goto the throttle body and try to open the throttle plates more by hand by turning the throttle lever the cable attaches to. If it doesn't move then its fine, if it does open more, then either get a new cable, or do the following.
First determine how much shorter the cable needs to be, an approximation is fine. You can either use zip ties, washers or something else that will stay put. To install the spacers, you'll want to detach the cable from the pedal and put enough spacers between the cable and the pedal to 'shorten' the cable by about the length you figured earlier.
Despite what anyone says, I see them say it a lot. Just because you can lift your pedal and create slack in the cable, doesn't mean it's stretched beyond tolerance. You'll see people all the time talking about putting washers or zipties on their throttle cables and having the vehicle become so much more responsive. Most of these are garbage, some actually have a problem where the throttle wasn't being fully opened, most are not. That slack is there for a reason, and its specifically designed to be that way. Take a look at that throttle lever, you you think it would stand up to a 200lb man stomping on it? probably not for long. If you look carefully, the pedal assembly itself bottoms out on something, either the floor or the firewall usually. This way when heman stomps on the pedal, a steel bar and the floor take the impact, not that thin cable and the tiny throttle lever. All these guys who claim they get more response are saying that because they think they should get more response. All they're really experiencing is the pedal opening the throttle a little sooner in relation to its distance from the floor. It 'feels' more responsive because they don't have to push the pedal as far, but the throttle can only open so far, if it was opening all the way when the pedal touched the floor, how can shortening the cable cause the throttle to open past its own limit?
Like I said, some people do have a legitimate problem where the throttle isn't actually opening all the way, but they are a minority of the cases.