Before the outline promote is run you will need to handle the Heading 1 to change its style to Title. This should be done with a Find and Replace. If you are using a macro, this would do it
Code:
Sub Macro2()
With ActiveDocument.Range.Find
.ClearFormatting
.Style = ActiveDocument.Styles("Heading 1")
.Replacement.ClearFormatting
.Replacement.Style = ActiveDocument.Styles("Title")
.Text = ""
.Wrap = wdFindContinue
.Format = True
.Execute Replace:=wdReplaceAll
End With
ActiveDocument.Range.Paragraphs.OutlinePromote
End Sub