Right click on your current namespace and select Refactor -> Rename and change the name in the pop up that comes up after a while. Enter your new name and click ok.
If you have multiple depths to your namespace, then Visual Studio won’t let you type a dot. However, if you copy and paste a dot, despite a warning, it will do the business.
To completely change to the new name, you will likely need to make additional changes manually. You can find where by performing a project search (ctrl+shift+f) for other references to the name in the Project, Solution, or other supporting files from a separate text editor like VS Code. Finally, folders may need to be changed manually as well.