It's probably held on with a socket cap screw. The bolt will have a hex shape cut in it. Use a hex wrench of the correct size, I think 1/4".
You will need to use the long end of the wrench. The screw may be too tight to loosen with the leverage you can muster with the short end of the wrench. Use a small pipe or adjustable wrench on the short hex to help you. Remember, lefty loosey righty tighty [;)]