McAfee Online Backup uses predefined backup sets to automatically identify files that should be included in a backup. You can also create custom backup sets. When a backup set is selected, any new or updated files that match that backup set's definition are automatically selected for backup.
If you cannot change this setting and you use Windows, you may be able to resolve this issue yourself. For more information, see If Settings Are Greyed Out in the McAfee Online Backup Backup Software for Windows. You may not be able to change this setting if your account administrator is managing it for you.
For more information, see Choosing Files to Back Up.