A treaty may be amended by the agreement of the Parties. Every Party to a treaty is entitled to participate in the amendment’s negotiations and to become a Party to the new amendment.
Parties are not required to adopt amendments. In fact, in accordance with the Vienna Convention on the Law of Treaties (part IV), the pre-amendment terms remain binding for any Party that does not adopt the amendment, even in dealings with a Party that is bound by the amendment.
Article 14 concerns amendments to the Convention and to annexes: who can propose them (para. 1), the process for submission (para. 2), how they are to be adopted (para. 3) and how they enter into force (paras. 4, 5 and 6).
For a more detailed description of the amendment procedure, see the Implementation Guide to the Convention, pages 146-147.