Click on the gear icon below the star icon on a project to open the Project Properties panel. If you are inside a project, you can access its properties by clicking on the Settings button at the top right corner of the screen.
Click on the Project Name to edit it.
Note:
Project admins and members can edit a public project's name.
Only the project admins can edit a private project's name.
Here's the link to the complete Workspace roles.