If you don't need them, you can delete installer files. If you plan on reinstalling OS X from scratch (or should you need to uninstall and reinstall a specific application), having installers in a folder on an external hard drive can come in han. To save a file or image on your computer or device, download it. The file will be saved in your default download location. On your computer, open Chrome. Go to the webpage where you want to download the file. Save the file: Most files: Click on the download link. Or, right-click on the file and choose Save as. Dec 27, 2006 No, you do not need to keep the.dmg file. I presume you've already double-clicked the file and followed through whatever installation process was presented to you(?). If so, the application will be installed - probably in your Applications folder - so you can. When you change a file's extension, you change the way programs on your computer read the file. The problem is, changing the file extension does not change the file format. If you have helpful information about the.dmg file extension, write to us! Rate our DMG page. Please help us by rating our DMG page on a 5-star rating system below.