Web- being already inside of the project, go to "Settings" on the right menu side and there you will be able to change the name of your project (1st picture).
Windows 10- open a project, look for "Project settings" icon on the top menu bar; click it, rename the project.
Mac- open the project, navigate to top menu and choose "File" and then "Settings" (2nd and 3rd picture).
Android- go to Your project list and tap on a certain project, a menu will pop up, choose "Rename".
P. S. Concerning Android, You can also rename the project while working on it; tap on three vertical dots icon on the top right, a menu will appear, choose "Settings".