Menu: View→Interface Properties→Misc
Selects the number of backup copies of the path diagram to keep.
See How backups work.
Programming
In Amos Graphics programs, you can select the first item in this ComboBox as follows (Visual Basic):
Dim aComboBox As Windows.Forms.ComboBox = pd.GetComboBox("InterfacePropertiesForm", "MiscOptCombo")
aComboBox.SelectedIndex = 0