You can change the format of a picture on Mac using Preview, the built-in image viewer and editor on your Mac. Preview is sufficient for most basic image conversion needs, such as converting to JPEG, JPEG 2000, PD, PNG, PSD, TIFF. However, if you need to convert images to JPG, or WEBP, consider a third-party app like iBoysoft MagicMenu. Follow the steps below to convert images on Mac using Preview: 1. Open the file you want to convert in the Preview app. 2. Choose File > Export from the top-left menu bar. 3. Choose a file type and click Save.