The Constitutional Convention of 1787

If you could go back to the Constitutional Convention of 1787 and make one change to the document, what would it be? Why? In preparing your answer, you should consider the actual circumstances that existed in that time. For example, if you want to outlaw slavery, is there any possibility that your version of the Constitution would have successfully entered into force? If not, would it be worth imposing the change if it meant failure in gaining ratification?