You can also upload an entirely separate project into a current one by accessing File > Upload from your computer in the editor and selecting and loading the desired project. Then, the project will keep its statistics and project id yet still change into an updated version. To get the file of your old project, go to your old project, and do the following: "File > Download to your computer.
Warning: Your old project will be lost forever if you overwrite your project with a new one. To avoid overwriting your old project once you have edited it, use Save As a Copy before uploading the new project.