If you want to change what a Set is backing up or if you get an error message such as:
Backup source does not exist
1. In the UI select Backup sets
2. Select the Set you want to edit
3. Select Source and, "I would like to choose the files to back up"
4. Check Select files then Expand the folders until you files or folder you wish to edit in the section to the right.
5. Check the files you want to back up and uncheck the files you no longer want to backup or that the error message is saying no longer exists.