NVivo 11 for Windows can be installed without uninstalling older versions of NVivo. NVivo 11, NVivo 10 and NVivo 9 are separate programs, which can be used independently.
After uninstalling any older version of NVivo program, you will be able to open and continue to work on any of your existing projects in NVivo 11.
Note: Any project files created in earlier versions can be opened in NVivo 11. However, projects created in NVivo 11 cannot be opened in any previous versions of the Software