500px does not have tools for backing up and restoring batches of photos. We suggest using a backup service to keep your photos safe, in addition to sharing them on 500px. However, there are some options to download your photos if needed.
1. You can download your photos if they are high-resolution by going to your Store settings at http://500px.com/settings/store and clicking on the high-resolution option down the centre column on the screen.
2. Another option is if you enable your photos for Creative Common license you can download a ~2048px size file of the image.