Making amendments to the constitution can be done a few different ways.
In order for an amendment to be added it is proposed by congress and earns a 2/3's approval or it is Proposed by a national convention and 2/3's of the states approve it. Once it passes this stage it goes on to the ratification, or the final approval. From here 2/4 of state legislature ratifies it or 3/4 of a special state convention approves it. This is a long process and once it is completed a new amendment will be added to the US constitution. A total of 17 amendments have been added this way since the ratification of the US constitution.