aplicación ya está en ejecución

Public Function get_aplicacion_existe() As Boolean
Dim appName As String = Process.GetCurrentProcess.ProcessName
        Dim sameProcessTotal As Integer = Process.GetProcessesByName(appName).Length
        MessageBox.Show(sameProcessTotal)
        If sameProcessTotal > 1 Then
            Return 1
        Else
            Return 0
        End If
End Function

Eliminar un proceso

Try
    For Each proc As Process In Process.GetProcessesByName("libros")
        proc.Kill()
    Next
  Catch ex As Exception
    MessageBox.Show(e.ToString)
  End Try