How to rename a state

How can I rename a state?
The Name field is not editable.
The state is already used by a lot of Tasks and User Stories.

Or is there any whay to add a new state and update all Tasks/User Stories to the new state at once?

You can't edit the State name in Azure DevOps. you can create your own state and use it instead of other state, in the state screen you have + New State button, just click it and add the new state (after you created the state you can't change his name!).

If you want to move current work items to the new state, you can create a query that returns the work items, then mark all and edit to the new state.