Article V: Amending the Constitution
The Constitution can be amended, or changed. The Constitution provides two ways in which it can be amended. First, Congress can propose amendments when 2/3rds of both houses agree. Secondly, when 2/3rds of the state legislatures apply for a convention call, Congress must call a convention for proposing amendments to the Constitution.
Proposed amendments must be ratified by 3/4ths of the states in order to be ratified and become part of the Constitution. No amendment banning the slave trade would be allowed until after 1808.
The Bill of Rights and other amendments to the Constitution were ratified following this procedure.