Dim lPos As Long
With RichTextBox1
  lPos = InStr(.Text, vbCrLf)
  If lPos > 0 Then 
    .SelStart = 0: .SelLength = lPos + 1
    .SelText = ""
  End If
 
  lPos = InStrRev(.Text, vbCrLf)
  If lPos > 0 Then
    .SelStart = lPos - 1
    .SelLength = Len(.Text)
    .SelText = ""
  End If
End With