This dialog box appears if you try to open a project created with earlier IntelliJ IDEA version.
|Convert to the new format now. You will not be able to open the project by earlier versions of IntelliJ IDEA||Select this option to convert the project to the new format. IntelliJ IDEA will back up old versions of project files to projectFilesBackUp folder within your project, so you could easily return to the old project version by replacing the project files with the old ones.|
|Convert later. Some features will be unavailable until you convert the project.||Select this option if you plan to work with this project using earlier IntelliJ IDEA versions. Some new features will be unavailable.|