Right-click the root folder of your project and selectfrom the context menu or press Shift+F6.
In the dialog that opens, choose the rename strategy.
If the project name is the same as the name of its root folder, select Rename directory.
If the project name is different from the name of its root folder, select Rename project. Also select this option if your application is deployed to a remote server and the project root folder is mapped to the server root.
Of course, you can rename the root folder and update the mapping in the server configuration accordingly, see Configuring synchronization with a web server for details.