How do you amend the constitution?

By the approval in Congress or in a Constitutional Convention.

Explanation:

It is possible to amend the Constitution by the Congress with a two-thirds majority vote in both the House of Representatives and the Senate or by a constitutional convention called for by two-thirds of the State legislatures. In those conventions, an amendment can be approved either by direct approval of the amendment or the approval via ratifying conventions.  

cannabis

explanation:

(assuming this is the us) google it. law states you can't have weed.