It seems like a pretty intuitive thing to do. They could even invalidate various treaties they have signed.
The UN charter is really hard to amend
It requires approval by two-thirds of its member states, and ratification by two-thirds of its member states, including in both cases by the five permanent members of the security council (the USA, the UK, Russia, China, and France). It's happened a total of 3 times, in each case, for completely non-controversial reasons.