Go to that person's page, and you should see a link "cancel friend request".
friends request overlimit

On your "Friends" page, on the right side, you will see a list of all the friends requests members have sent you that you haven't yet accepted or decline,
then under that, there will be a list of all of the friends requests you've sent to others. Those are the ones not yet accepted by the other person, so you need to cancel some of those before sending out anymore friends requests.

You may find this algorithm for making new friends - illustrated by a video (based on the experience of Stu the Cockatoo - he's new at the zoo) - illuminating.
I have 20 friend requests that people haven't responded to. I can't ask anyone else until these are gone. How do I eliminate those requests that people are ignoring?
Bill