Sub ChangeParasAfterHeading()
Dim para As Paragraph, nextPara As Paragraph
Dim oRng As Range
    If Selection.Type = wdSelectionIP Then
        MsgBox Prompt:="You have not selected any text!"
        Exit Sub
    End If
    Set oRng = Selection.Range
    With oRng
        For Each para In oRng.Paragraphs
            Select Case para.Style
                Case Is = "Heading 1"
                    Set nextPara = para.Next
                    If Not nextPara Is Nothing Then
                        nextPara.Style = "Body1"
                    End If
                Case Is = "Heading 2"
                    Set nextPara = para.Next
                    If Not nextPara Is Nothing Then
                        nextPara.Style = "Body2"
                    End If
                Case Else
            End Select
        Next para
    End With
End Sub