Delta Sync is a feature that allows you to sync your data (including games, save files, skins, and BIOS files) with either Google Drive or Dropbox.
To enable, go to 'Delta Sync' in your settings and tap on 'Service' to select either Google Drive or Dropbox. Just sign into your account, and Delta will immediately begin syncing your data.
A new 'Sync Status' line will appear in your Delta Sync settings once you have connected a service to help you resolve any issues that may arise.
Delta files are not visible in Google Drive. They are visible in Dropbox, but they are not intended to be edited as this may cause data loss.